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<h1 class="mume-header" id="733-flood-fillhttpsleetcodecomproblemsflood-fill"><a href="https://leetcode.com/problems/flood-fill/">733. Flood Fill</a> 🌟</h1>
<p>An image is represented by an m x n integer grid image where image[i][j] represents the pixel value of the image.</p>
<p>You are also given three integers sr, sc, and newColor. You should perform a flood fill on the image starting from the pixel image[sr][sc].</p>
<p>To perform a flood fill, consider the starting pixel, plus any pixels connected 4-directionally to the starting pixel of the same color as the starting pixel, plus any pixels connected 4-directionally to those pixels (also with the same color), and so on. Replace the color of all of the aforementioned pixels with newColor.</p>
<p>Return the modified image after performing the flood fill.</p>
<h3 class="mume-header" id="dfs-recursive">DFS - Recursive</h3>
<ul>
<li>
<p><strong>Main function:</strong></p>
<ul>
<li>if current color is not new color, call the dfs algorithm.</li>
<li>else return original image.</li>
</ul>
</li>
<li>
<p><strong>DFS function:</strong></p>
<ul>
<li>check for invalid row and column numbers.</li>
<li>check if current color is not old color or is already new color.</li>
<li>for both the cases return.</li>
<li>set current color to new color.</li>
<li>call the function for all the 4 directions.</li>
</ul>
</li>
<li>
<p><strong>Complexity:</strong></p>
<ul>
<li>Time: <strong>O(M * N)</strong>, where <code>M <= 50</code> is number of rows, <code>N <= 50</code> is number of columns in the matrix.</li>
<li>Space: <strong>O(M * N)</strong>, it's the depth stack memory, in worst case is <strong>O(M * N)</strong>, can check this discussion on <a href="https://stackoverflow.com/a/50912382/4084297">stackoverflow</a>.</li>
</ul>
</li>
</ul>
<h3 class="mume-header" id="code">Code</h3>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span><span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
vector<span class="token operator"><</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">>></span> <span class="token function">floodFill</span><span class="token punctuation">(</span>vector<span class="token operator"><</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">>></span> <span class="token operator">&</span>image<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> sr<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> sc<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> newColor<span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>image<span class="token punctuation">[</span>sr<span class="token punctuation">]</span><span class="token punctuation">[</span>sc<span class="token punctuation">]</span> <span class="token operator">!=</span> newColor<span class="token punctuation">)</span>
<span class="token function">dfs</span><span class="token punctuation">(</span>image<span class="token punctuation">,</span> sr<span class="token punctuation">,</span> sc<span class="token punctuation">,</span> newColor<span class="token punctuation">,</span> image<span class="token punctuation">[</span>sr<span class="token punctuation">]</span><span class="token punctuation">[</span>sc<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-return">return</span> image<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-private">private</span><span class="token operator">:</span>
<span class="token keyword keyword-void">void</span> <span class="token function">dfs</span><span class="token punctuation">(</span>vector<span class="token operator"><</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">>></span> <span class="token operator">&</span>imgs<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> r<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> c<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> newColor<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> oldColor<span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// invalid row or column</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>r <span class="token operator"><</span> <span class="token number">0</span> <span class="token operator">||</span> c <span class="token operator"><</span> <span class="token number">0</span> <span class="token operator">||</span> r <span class="token operator">>=</span> imgs<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">||</span> c <span class="token operator">>=</span> imgs<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span><span class="token punctuation">;</span>
<span class="token comment">// current color is not old color or is already new color</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>imgs<span class="token punctuation">[</span>r<span class="token punctuation">]</span><span class="token punctuation">[</span>c<span class="token punctuation">]</span> <span class="token operator">!=</span> oldColor <span class="token operator">||</span> imgs<span class="token punctuation">[</span>r<span class="token punctuation">]</span><span class="token punctuation">[</span>c<span class="token punctuation">]</span> <span class="token operator">==</span> newColor<span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span><span class="token punctuation">;</span>
imgs<span class="token punctuation">[</span>r<span class="token punctuation">]</span><span class="token punctuation">[</span>c<span class="token punctuation">]</span> <span class="token operator">=</span> newColor<span class="token punctuation">;</span> <span class="token comment">// for next we can also use dirs vector.</span>
<span class="token function">dfs</span><span class="token punctuation">(</span>imgs<span class="token punctuation">,</span> r <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">,</span> c<span class="token punctuation">,</span> newColor<span class="token punctuation">,</span> oldColor<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// up</span>
<span class="token function">dfs</span><span class="token punctuation">(</span>imgs<span class="token punctuation">,</span> r <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">,</span> c<span class="token punctuation">,</span> newColor<span class="token punctuation">,</span> oldColor<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// down</span>
<span class="token function">dfs</span><span class="token punctuation">(</span>imgs<span class="token punctuation">,</span> r<span class="token punctuation">,</span> c <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">,</span> newColor<span class="token punctuation">,</span> oldColor<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// left</span>
<span class="token function">dfs</span><span class="token punctuation">(</span>imgs<span class="token punctuation">,</span> r<span class="token punctuation">,</span> c <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">,</span> newColor<span class="token punctuation">,</span> oldColor<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// right</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><hr>
<h3 class="mume-header" id="bfs-iterative">BFS - Iterative</h3>
<ul>
<li>
<p><strong>Main function:BFS</strong></p>
<ul>
<li>if current color is already new color, return original image</li>
<li>We need a 2D direction vector and a queue for BFS (q of pairs).</li>
<li>push starting point in the queue.</li>
<li>while queue is not empty run loop.
<ul>
<li>get the row and column index form the front of the queue, and pop it.</li>
<li>set current color to new color</li>
<li>for all directions push {r,c} in the queue if it's valid.</li>
</ul>
</li>
</ul>
</li>
<li>
<p><strong>Complexity:</strong></p>
<ul>
<li>Time: <strong>O(M * N)</strong>, where <code>M <= 50</code> is number of rows, <code>N <= 50</code> is number of columns in the matrix.</li>
<li>Space: <strong>O(M * N)</strong>, it's the depth stack memory, in worst case is <strong>O(M * N)</strong>, can check this discussion on <a href="https://stackoverflow.com/a/50912382/4084297">stackoverflow</a>.</li>
</ul>
</li>
</ul>
<h3 class="mume-header" id="code-1">Code</h3>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span><span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
vector<span class="token operator"><</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">>></span> <span class="token function">floodFill</span><span class="token punctuation">(</span>vector<span class="token operator"><</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">>></span> <span class="token operator">&</span>image<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> sr<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> sc<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> newColor<span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> currColor <span class="token operator">=</span> image<span class="token punctuation">[</span>sr<span class="token punctuation">]</span><span class="token punctuation">[</span>sc<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token comment">// if current color is already new color, return original image</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>currColor <span class="token operator">==</span> newColor<span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> image<span class="token punctuation">;</span>
<span class="token comment">// UNCOMMENT BELOW LINE</span>
<span class="token keyword keyword-const">const</span> vector<span class="token operator"><</span>pair<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span><span class="token operator">>></span> dirs <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">{</span><span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">}</span><span class="token punctuation">}</span><span class="token punctuation">;</span> <span class="token comment">// directions vector</span>
queue<span class="token operator"><</span>pair<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span><span class="token operator">>></span> q<span class="token punctuation">;</span> <span class="token comment">// queue for bfs</span>
q<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">{</span>sr<span class="token punctuation">,</span> sc<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// push starting point</span>
<span class="token comment">// while queue is not empty run loop.</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span><span class="token operator">!</span>q<span class="token punctuation">.</span><span class="token function">empty</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token comment">// get the row and column index form the front of the queue, and pop it.</span>
<span class="token keyword keyword-int">int</span> row <span class="token operator">=</span> q<span class="token punctuation">.</span><span class="token function">front</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>first<span class="token punctuation">,</span> col <span class="token operator">=</span> q<span class="token punctuation">.</span><span class="token function">front</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>second<span class="token punctuation">;</span>
q<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// set current color to new color</span>
image<span class="token punctuation">[</span>row<span class="token punctuation">]</span><span class="token punctuation">[</span>col<span class="token punctuation">]</span> <span class="token operator">=</span> newColor<span class="token punctuation">;</span>
<span class="token comment">// for all directions push {r,c} in the queue if it's valid.</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-auto">auto</span> <span class="token operator">&</span>x <span class="token operator">:</span> dirs<span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> r <span class="token operator">=</span> row <span class="token operator">+</span> x<span class="token punctuation">.</span>first<span class="token punctuation">,</span> c <span class="token operator">=</span> col <span class="token operator">+</span> x<span class="token punctuation">.</span>second<span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>r <span class="token operator"><</span> <span class="token number">0</span> <span class="token operator">||</span> c <span class="token operator"><</span> <span class="token number">0</span> <span class="token operator">||</span> r <span class="token operator">>=</span> image<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">||</span> c <span class="token operator">>=</span> image<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">||</span> image<span class="token punctuation">[</span>r<span class="token punctuation">]</span><span class="token punctuation">[</span>c<span class="token punctuation">]</span> <span class="token operator">!=</span> currColor<span class="token punctuation">)</span>
<span class="token keyword keyword-continue">continue</span><span class="token punctuation">;</span>
q<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">{</span>r<span class="token punctuation">,</span> c<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> image<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><h3 class="mume-header" id="must-reads">MUST READS:</h3>
<ul>
<li>
<p><a href="https://leetcode.com/problems/flood-fill/discuss/442143/How-do-you-think-about-solving-a-question-using-DFS-Learn-before-you-Code">How do you think about solving a question using DFS [ Learn before you Code ]</a></p>
</li>
<li>
<p><a href="https://leetcode.com/problems/flood-fill/discuss/627915/C%2B%2B-standard-solution-schema-you-can-apply-to-other-tasks%3A-list-%2B-visited">[C++] standard solution, schema you can apply to other tasks: list + visited</a></p>
</li>
</ul>
</div>
</body></html>