path-sum

题目描述:

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:
Given the below binary tree andsum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \      \
        7    2      1

return true, as there exist a root-to-leaf path5->4->11->2which sum is 22.

/**
 * Definition for binary tree
 * 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) {
        if(!root) return false;
        
        if(root->left == NULL && root->right == NULL){
            if(root->val == sum)
                return true;
            else 
                return false;       
        }
        
        bool res = hasPathHelp(root,sum,0);
        return res;
    }
    
    bool hasPathHelp(TreeNode *root,int sum,int curSum){
        if(!root)    return false;
        
        if(root->left == NULL && root->right == NULL){
            if(curSum + root->val == sum)
                return true;
            else 
                return false;
        }
        
        return hasPathHelp(root->left,sum,curSum+root->val)||hasPathHelp(root->right,sum,curSum+root->val);
    }
};