[정현준] 13주차

house-robber/jdalma.kt

@@ -0,0 +1,65 @@
+package leetcode_study
+
+import io.kotest.matchers.shouldBe
+import org.junit.jupiter.api.Test
+import kotlin.math.max
+
+class `house-robber` {
+
+    fun rob(nums: IntArray): Int {
+        return usingDP(nums)
+    }
+
+    /**
+     * TC: O(n), SC: O(n)
+     */
+    private fun usingDP(nums: IntArray): Int {
+        val dp = IntArray(nums.size + 1).apply {
+            this[0] = 0
+            this[1] = nums[0]
+        }
+        for (index in 1 until nums.size) {
+            dp[index + 1] = max(nums[index] + dp[index - 1], dp[index])
+        }
+
+        return dp[nums.size]
+    }
+
+    /**
+     * TC: O(n), SC: O(n)
+     */
+    private fun usingMemoization(nums: IntArray): Int {
+        val memo = IntArray(nums.size) { -1 }
+        fun recursive(index: Int): Int {
+            return if (index > nums.size - 1) 0
+            else if (memo[index] != -1) memo[index]
+            else {
+                memo[index] = max(nums[index] + recursive(index + 2), recursive(index + 1))
+                memo[index]
+            }
+        }
+
+        return recursive(0)
+    }
+
+    /**
+     * 시간초과
+     * TC: O(2^n), SC: O(n)
+     */
+    private fun usingRecursive(nums:IntArray): Int {
+        fun recursive(index: Int, depth: Int): Int {
+            if (index > nums.size - 1) return 0
+            println("${"-".repeat(depth)} : max($index + ${index + 2}, ${index + 1})")
+            return max(nums[index] + recursive(index + 2, depth + 1), recursive(index + 1, depth + 1))
+        }
+
+        return recursive(0, 0)
+    }
+
+    @Test
+    fun `인접하지 않은 원소를 선택하여 최대의 합을 반환한다`() {
+        rob(intArrayOf(1,2,3,1)) shouldBe 4
+        rob(intArrayOf(2,7,9,3,1)) shouldBe 12
+        rob(intArrayOf(8,7,9,11,1)) shouldBe 19
+    }
+}

lowest-common-ancestor-of-a-binary-search-tree/jdalma.kt

@@ -0,0 +1,40 @@
+package leetcode_study
+
+import io.kotest.matchers.shouldBe
+import org.junit.jupiter.api.Test
+import kotlin.math.max
+import kotlin.math.min
+
+class `lowest-common-ancestor-of-a-binary-search-tree` {
+
+    /**
+     * TC: O(log n), SC: O(1)
+     */
+    fun lowestCommonAncestor(root: TreeNode?, p: TreeNode?, q: TreeNode?): TreeNode? {
+        if (p == null || q == null) return null
+
+        var node = root
+        val max = max(p.`val`, q.`val`)
+        val min = min(p.`val`, q.`val`)
+
+        while (node != null) {
+            node = if (node.`val` > max) {
+                node.left
+            } else if (node.`val` < min) {
+                node.right
+            } else {
+                return node
+            }
+        }
+        return null
+    }
+
+    @Test
+    fun `가장 낮은 값의 공통 조상을 반환한다`() {
+        lowestCommonAncestor(
+            TreeNode.of(6,2,8,0,4,7,9,null,null,3,5),
+            TreeNode(2),
+            TreeNode(8)
+        )!!.`val` shouldBe 6
+    }
+}

meeting-rooms/jdalma.java

@@ -0,0 +1,79 @@
+package leetcode;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+public class jdalma {
+
+    public class Interval {
+        public int start, end;
+
+        public Interval(int start, int end) {
+            this.start = start;
+            this.end = end;
+        }
+    }
+
+    public boolean canAttendMeetings(List<Interval> intervals) {
+        return usingBruteForce(intervals);
+    }
+
+    /**
+     * TC: O(n^2), SC: O(1)
+     */
+    private boolean usingBruteForce(List<Interval> intervals) {
+        final int size = intervals.size();
+        for (int i = 0; i < size; i++) {
+            Interval A = intervals.get(i);
+            for (int j = i + 1; j < size; j++) {
+                Interval B = intervals.get(j);
+                if (Math.min(A.end, B.end) > Math.max(A.start, B.start)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    /**
+     * TC: O(n log n), SC: O(1)
+     */
+    private boolean usingSort(List<Interval> intervals) {
+        intervals.sort(Comparator.comparingInt(i -> i.start));
+
+        for (int i = 1; i < intervals.size(); i++) {
+            Interval first = intervals.get(i - 1);
+            Interval second = intervals.get(i);
+
+            if (first.end > second.start) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    @Test
+    @DisplayName("입력받은 간격들의 충돌 여부를 반환한다.")
+    void name() {
+        Assertions.assertThat(canAttendMeetings(new ArrayList<>() {
+            {
+                add(new Interval(0, 30));
+                add(new Interval(5, 10));
+                add(new Interval(15, 20));
+            }
+        })).isFalse();
+
+        Assertions.assertThat(canAttendMeetings(new ArrayList<>() {
+            {
+                add(new Interval(5, 8));
+                add(new Interval(9, 10));
+            }
+        })).isTrue();
+    }
+}