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0303-range-sum-query---immutable/README.md

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+<p>Given an integer array <code>nums</code>, handle multiple queries of the following type:</p>
+
+<ol>
+	<li>Calculate the <strong>sum</strong> of the elements of <code>nums</code> between indices <code>left</code> and <code>right</code> <strong>inclusive</strong> where <code>left &lt;= right</code>.</li>
+</ol>
+
+<p>Implement the <code>NumArray</code> class:</p>
+
+<ul>
+	<li><code>NumArray(int[] nums)</code> Initializes the object with the integer array <code>nums</code>.</li>
+	<li><code>int sumRange(int left, int right)</code> Returns the <strong>sum</strong> of the elements of <code>nums</code> between indices <code>left</code> and <code>right</code> <strong>inclusive</strong> (i.e. <code>nums[left] + nums[left + 1] + ... + nums[right]</code>).</li>
+</ul>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input</strong>
+[&quot;NumArray&quot;, &quot;sumRange&quot;, &quot;sumRange&quot;, &quot;sumRange&quot;]
+[[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]
+<strong>Output</strong>
+[null, 1, -1, -3]
+
+<strong>Explanation</strong>
+NumArray numArray = new NumArray([-2, 0, 3, -5, 2, -1]);
+numArray.sumRange(0, 2); // return (-2) + 0 + 3 = 1
+numArray.sumRange(2, 5); // return 3 + (-5) + 2 + (-1) = -1
+numArray.sumRange(0, 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= nums.length &lt;= 10<sup>4</sup></code></li>
+	<li><code>-10<sup>5</sup> &lt;= nums[i] &lt;= 10<sup>5</sup></code></li>
+	<li><code>0 &lt;= left &lt;= right &lt; nums.length</code></li>
+	<li>At most <code>10<sup>4</sup></code> calls will be made to <code>sumRange</code>.</li>
+</ul>

0303-range-sum-query---immutable/solution.py

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+# Approach 3: Prefix Sum
+
+# Time: O(1)
+# Space: O(n)
+
+class NumArray:
+
+    def __init__(self, nums: List[int]):
+        self.prefix_sum = [0] * (len(nums) + 1)
+        for i in range(len(nums)):
+            self.prefix_sum[i + 1] = self.prefix_sum[i] + nums[i]
+
+    def sumRange(self, left: int, right: int) -> int:
+        return self.prefix_sum[right + 1] - self.prefix_sum[left]
+
+
+
+# Your NumArray object will be instantiated and called as such:
+# obj = NumArray(nums)
+# param_1 = obj.sumRange(left,right)