sum.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
#include <stack>
using namespace std;

class Solution {
public:
    bool hasPathSum(TreeNode* root, int sum) {
        if(!root) return false;
        
        stack<TreeNode*> trail;
        stack<int> sums;
        trail.push(root);
        sums.push(root->val);
        
        while( !trail.empty()){
            
            TreeNode* current = trail.top();
            int current_sum = sums.top();
            trail.pop();
            sums.pop();
            
            if(!(current->left || current->right) && current_sum==sum ) return true;
            if(current->left){
                trail.push(current->left);
                sums.push(current_sum + current->left->val);
            }
            if(current->right){
                trail.push(current->right);
                sums.push(current_sum + current->right->val);
            } 
        }
        
        return false;
    }
};