leetcode 543. The diameter of a binary tree-java solution

Topic category

binary tree

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Given a binary tree, you need to calculate its diameter length. The diameter of a binary tree is the maximum of the lengths of the paths between any two nodes. This path may or may not pass through the root node.

Code case: 1
/
2 3
/ \
4 5

Returns 3, whose length is the path [4,2,1,3] or [5,2,1,3].

answer

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    
    
    int ans = 0 ;
    public int diameterOfBinaryTree(TreeNode root) {
    
    
        dfs(root);
        return ans ;
    }
    public int dfs(TreeNode root){
    
    
        if(root == null) return 0 ;
        int left = dfs(root.left);
        int right = dfs(root.right);
        ans = Math.max(ans , left + right );
        return Math.max(left ,right)+1;
    }
}