https://leetcode.com/problems/sum-root-to-leaf-numbers/

Medium

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Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

Note: A leaf is a node with no children.

Example:

Input: [1,2,3]
    1
   / \
  2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   / \
  9   0
 / \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

 

这么快出了一个medium 还是很开心的

除了特判一定记得！！

/**
 * 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 sum;
    void cal(TreeNode* p, int cnt) {
        if (p == NULL) {
            return;
        }
        cnt = cnt * 10 + p->val;
        printf("val=%d,cnt=%d\n", p->val, cnt);
        if (p->left) {
            cal(p->left, cnt);
        }
        if (p->right) {
            cal(p->right, cnt);
        }
        if (p->left == NULL && p->right == NULL) {
            sum +=cnt;
        }
    }
    int sumNumbers(TreeNode* root) {
        sum = 0;
        cal(root, 0);
        return sum;
    }
};