[hsskey] Week 14 Solutions

binary-tree-level-order-traversal/hsskey.js

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+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val === undefined ? 0 : val);
+ *     this.left = (left === undefined ? null : left);
+ *     this.right = (right === undefined ? null : right);
+ * }
+ */
+
+/**
+ * @param {TreeNode} root
+ * @return {number[][]}
+ */
+var levelOrder = function(root) {
+    const res = [];
+    if (!root) return res;
+
+    const q = [root];
+
+    while (q.length > 0) {
+        const qLen = q.length;
+        const level = [];
+
+        for (let i = 0; i < qLen; i++) {
+            const node = q.shift();
+            if (node) {
+                level.push(node.val);
+                if (node.left) q.push(node.left);
+                if (node.right) q.push(node.right);
+            }
+        }
+
+        if (level.length > 0) {
+            res.push(level);
+        }
+    }
+
+    return res;
+};
+

counting-bits/hsskey.js

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+/**
+ * @param {number} n
+ * @return {number[]}
+ */
+var countBits = function(n) {
+    const dp = new Array(n + 1).fill(0);
+    let offset = 1;
+
+    for (let i = 1; i <= n; i++) {
+        if (offset * 2 === i) {
+            offset = i;
+        }
+        dp[i] = 1 + dp[i - offset];
+    }
+
+    return dp;
+};
+

house-robber-ii/hsskey.js

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+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var rob = function(nums) {
+    if (nums.length === 1) return nums[0];
+
+    const helper = (snums) => {
+        let rob1 = 0,
+            rob2 = 0;
+
+        for (let n of snums) {
+            const newRob = Math.max(rob1 + n, rob2);
+            rob1 = rob2;
+            rob2 = newRob;
+        }
+
+        return rob2;
+    };
+
+    return Math.max(helper(nums.slice(1)), helper(nums.slice(0, -1)));
+};
+

meeting-rooms-ii/hsskey.js

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+export class Solution {
+    /**
+     * @param {Interval[]} intervals - an array of meeting time intervals
+     * @return {number} the minimum number of conference rooms required
+     */
+    minMeetingRooms(intervals) {
+        if (!intervals || intervals.length === 0) return 0;
+
+        const start = intervals.map(i => i.start).sort((a, b) => a - b);
+        const end = intervals.map(i => i.end).sort((a, b) => a - b);
+
+        let res = 0;
+        let count = 0;
+        let s = 0,
+            e = 0;
+
+        while (s < intervals.length) {
+            if (start[s] < end[e]) {
+                s += 1;
+                count += 1;
+            } else {
+                e += 1;
+                count -= 1;
+            }
+            res = Math.max(res, count);
+        }
+
+        return res;
+    }
+}
+

word-search-ii/hsskey.js

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+class TrieNode {
+    constructor() {
+        this.children = {};
+        this.isWord = false;
+    }
+
+    add(word) {
+        let node = this;
+        for (let ch of word) {
+            if (!node.children[ch]) {
+                node.children[ch] = new TrieNode();
+            }
+            node = node.children[ch];
+        }
+        node.isWord = true;
+    }
+}
+
+/**
+ * @param {character[][]} board
+ * @param {string[]} words
+ * @return {string[]}
+ */
+var findWords = function(board, words) {
+    const root = new TrieNode();
+    for (let word of words) {
+        root.add(word);
+    }
+
+    const ROWS = board.length;
+    const COLS = board[0].length;
+    const res = new Set();
+    const visit = new Set();
+
+    const dfs = (r, c, node, word) => {
+        if (
+            r < 0 || c < 0 ||
+            r >= ROWS || c >= COLS ||
+            visit.has(`${r},${c}`) ||
+            !node.children[board[r][c]]
+        ) return;
+
+        visit.add(`${r},${c}`);
+        node = node.children[board[r][c]];
+        word += board[r][c];
+
+        if (node.isWord) {
+            res.add(word);
+        }
+
+        dfs(r + 1, c, node, word);
+        dfs(r - 1, c, node, word);
+        dfs(r, c + 1, node, word);
+        dfs(r, c - 1, node, word);
+
+        visit.delete(`${r},${c}`);
+    };
+
+    for (let r = 0; r < ROWS; r++) {
+        for (let c = 0; c < COLS; c++) {
+            dfs(r, c, root, "");
+        }
+    }
+
+    return Array.from(res);
+};
+