leetcode 112 Path Sum 路径和

437 path sum

 C++:使用递归先序遍历，记录根节点到当前节点的路径和，如果当前节点是叶节点，判断是否等于sum

/**
 * 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:
    bool hasPathSum(TreeNode* root, int sum) {
        bool res=false;
        dfs(root,sum,0,res);
        return res;
    }
    void dfs(TreeNode* node,int sum,int curSum,bool &res){
        if(!node) return;
        curSum+=node->val;
        if(node->left==NULL&&node->right==NULL&&curSum==sum) res=true;
        dfs(node->left,sum,curSum,res);
        dfs(node->right,sum,curSum,res);
    }
};