543. Diameter of Binary Tree

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longestpath between any two nodes in a tree. This path may or may not pass through the root.

Example:

Given a binary tree 

1
/ \
2   3
/ \
4   5

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

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

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只要计算左右子树的深度即可
/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    int Search(TreeNode* root,int &ans)

{

if(root->left==NULL &&root->right==NULL)
{
return 0;
}

int l=0;
if(root->left)
{
l=Search(root->left,ans)+1;
}
int r=0;
if(root->right)
{
r=Search(root->right,ans)+1;
}
if(r+l>ans)
{
ans=r+l;
}
return max(l,r);

}

int diameterOfBinaryTree(TreeNode* root) {

        int ans = 0; 

        if(root){

            Search(root, ans); 

        }

        return ans; 

    }

};