Path Sum

每次用递归都怕栈溢出
 1 /**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
private: map<int,bool> sums;
public:
    bool hasPathSum(TreeNode *root, int sum) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root==NULL)
        return false;
        sums.clear();
        sums[sum] = false;
        addSum(root,0);
        return sums[sum];
    }
    
    void addSum(TreeNode *root,int pre)
    {
        if(root->left==NULL && root->right==NULL)
        {
            sums[pre+root->val] = true;
        }
        if(root->left!=NULL)
        {
            addSum(root->left,pre+root->val);
        }
        if(root->right!=NULL)
        {
            addSum(root->right,pre+root->val);
        }
    }
};