LeetCode题组：第543题-二叉树的直径

      1
     / \
    2   3
   / \     
  4   5    

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

int max (int a,int b) {
    return a > b ? a : b;
}
int travelTree(struct TreeNode * root, int * diameter) {
    if (root == NULL) {
        return 0;
    }
    int left = travelTree(root->left, diameter);
    int right = travelTree(root->right, diameter);
    *diameter = max(*diameter, left + right);
    return 1 + max(left, right);
}

int diameterOfBinaryTree(struct TreeNode* root){
    int diameter = 0;
    travelTree(root, &diameter);
    return diameter;
}