【leetcode】129. Sum Root to Leaf Numbers

最重要的关键就是当只有单亲孩子的时候，不能重复计数。

所以需要对当前结点是否有双亲孩子，单亲孩子，还有叶节点的分别考虑。主要问题在于重复计数。

/**
 *  @author         johnsondu
 *  @time           20:51 8th Oct 2015
 *  @type           binary tree traverse
 *  @url            https://leetcode.com/problems/sum-root-to-leaf-numbers/
 *  @status         Accepted
 */

/**
 * 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:
    void dfs(int cnt, TreeNode* node, int &ans) {
        cnt = cnt * 10 + node->val;
        if(node->left && node->right) {
            dfs(cnt, node->left, ans);
            dfs(cnt, node->right, ans);
        }
        else if(node->left) dfs(cnt, node->left, ans);
        else if(node->right) dfs(cnt, node->right, ans);
        else ans += cnt;
    }

    int sumNumbers(TreeNode* root) {
        int ans = 0;
        if(root == NULL) return ans;
        int cnt = root->val;
        if(root->left && root->right) {
            dfs(cnt, root->left, ans);
            dfs(cnt, root->right, ans);
        }
        else if(root->left) dfs(cnt, root->left, ans);
        else if(root->right) dfs(cnt, root->right, ans);
        else ans += cnt;
        return ans;
    }
};