[gitsunmin] Week12 Solutions

merge-intervals/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/merge-intervals/
+ * time complexity : O(n)
+ * space complexity : O(n)
+ */
+
+function merge(intervals: number[][]): number[][] {
+    if (intervals.length === 0) return [];
+
+    intervals.sort((a, b) => a[0] - b[0]);
+
+    const merged: number[][] = [];
+    for (const interval of intervals) {
+        if (merged.length === 0 || merged[merged.length - 1][1] < interval[0]) merged.push(interval);
+        else merged[merged.length - 1][1] = Math.max(merged[merged.length - 1][1], interval[1]);
+    }
+    return merged;
+};

remove-nth-node-from-end-of-list/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/remove-nth-node-from-end-of-list/
+ * time complexity : O(n)
+ * space complexity : O(1)
+ */
+
+class ListNode {
+    val: number
+    next: ListNode | null
+    constructor(val?: number, next?: ListNode | null) {
+        this.val = (val === undefined ? 0 : val)
+        this.next = (next === undefined ? null : next)
+    }
+}
+
+function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
+    const dummy = new ListNode(0, head);
+    let first: ListNode | null = dummy;
+    let second: ListNode | null = dummy;
+
+    for (let i = 0; i <= n; i++) {
+        if (first !== null) first = first.next;
+    }
+
+    while (first !== null) {
+        first = first.next;
+        second = second!.next;
+    }
+
+    if (second !== null && second.next !== null) second.next = second.next.next;
+
+    return dummy.next;
+};

same-tree/gitsunmin.ts

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+/**
+ * https://leetcode.com/problems/same-tree/
+ * time complexity : O(n)
+ * space complexity : O(n)
+ */
+
+class TreeNode {
+    val: number
+    left: TreeNode | null
+    right: TreeNode | null
+    constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+        this.val = (val === undefined ? 0 : val)
+        this.left = (left === undefined ? null : left)
+        this.right = (right === undefined ? null : right)
+    }
+}
+
+function isSameTree(p: TreeNode | null, q: TreeNode | null): boolean {
+    if (p === null && q === null) return true;
+    if (p === null || q === null) return false;
+    if (p.val !== q.val) return false;
+
+    return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
+};