feat: 每日一题更新答案 #687

Author: luzhipeng

Diff for: daily/answers/687.longest-univalue-path.js

@@ -0,0 +1,38 @@
+/*
+ * @lc app=leetcode id=687 lang=javascript
+ *
+ * [687] Longest Univalue Path
+ */
+
+// 返回经过root的且只能取左右一个节点的路径长度
+function helper(node, res) {
+    if (node === null) return 0;
+    const l = helper(node.left, res);
+    const r = helper(node.right, res);
+    let lcnt = 0;
+    let rcnt = 0;
+    if (node.left && node.val === node.left.val) lcnt = lcnt + l + 1;
+    if (node.right && node.val === node.right.val) rcnt = rcnt + r + 1;
+    
+    res.max = Math.max(res.max, lcnt + rcnt);
+    
+    return Math.max(lcnt, rcnt);
+  }
+  /**
+   * Definition for a binary tree node.
+   * function TreeNode(val) {
+   *     this.val = val;
+   *     this.left = this.right = null;
+   * }
+   */
+  /**
+   * @param {TreeNode} root
+   * @return {number}
+   */
+  var longestUnivaluePath = function(root) {
+    const res = {
+      max: 0
+    };
+    helper(root, res);
+    return res.max;
+  };