687. Longest Univalue Path(相同节点值的最大路径长度)
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.
方法一:递归
因为这道题求的是相同结点的最大路径,肯定需要从根节点遍历到尾部。遍历树一般用递归比较方便。递归调用是从根往子叶上调,但是返回是子叶往根返回。
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { private int path=0; public int longestUnivaluePath(TreeNode root) { dfs(root); return path; } private int dfs(TreeNode root){ if(root==null) return 0; int left=dfs(root.left); int right=dfs(root.right); int leftPath=root.left!=null&&root.left.val==root.val?left+1:0; //如果左孩子和父节点相同,则多了一条路径 int rightPath=root.right!=null&&root.right.val==root.val?right+1:0; //如果右孩子和父节点相同,则多了一条路径 path=Math.max(path,leftPath+rightPath); return Math.max(leftPath,rightPath); } }
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