687. Longest Univalue Path 最长的唯一路径

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Given a binary tree, find the length of the longest path where each node in the path has the same value. This path may or may not pass through the root.

Note: The length of path between two nodes is represented by the number of edges between them.

Example 1:

Input:

              5
             /             4   5
           / \             1   1   5

Output:

2

Example 2:

Input:

              1
             /             4   5
           / \             4   4   5

Output:

2

Note: The given binary tree has not more than 10000 nodes. The height of the tree is not more than 1000.

给定二叉树,找到路径中每个节点具有相同值的最长路径的长度。此路径可能通过或不能通过根。
  1. let max = 0;
  2. var longestUnivaluePath = function(root) {
  3. max = 0;
  4. helper(root, null);
  5. return max;
  6. };
  7. var helper = (node,parentVal) => {
  8. if (!node) return 0;
  9. let left = helper(node.left, node.val);
  10. let right = helper(node.right, node.val);
  11. max = Math.max(left + right, max);
  12. if (node.val == parentVal) {
  13. return Math.max(left, right) + 1;
  14. } else {
  15. return 0;
  16. }
  17. }






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