c_cpp 112. Path Sum - DifficultyEasy - 2018.9.11

Posted 2021-05-14

/**
 * 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) {
        if (root == NULL) {
            return false;
        }
        stack<TreeNode *> nodeS;
        nodeS.push(root);
        int addUp = root->val;
        TreeNode *preNode;        
        bool turningBack;
        while(!nodeS.empty()) {
            preNode = nodeS.top();
            if (preNode->left != NULL) {
                turningBack = false;
                addUp += preNode->left->val;
                nodeS.push(preNode->left);
                preNode->left = NULL;
                continue;
            }
            if (preNode->right != NULL) {
                turningBack = false;
                addUp += preNode->right->val;
                nodeS.push(preNode->right);
                preNode->right = NULL;
                continue;
            }
            if (addUp == sum 
                && !turningBack) {
                return true;
            }
            turningBack = true;
            addUp -= preNode->val;
            nodeS.pop();
        }
        return false;
    }
};