leetcode-Path Sum

Path Sum

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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 and sum = 22,

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

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

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/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:

    int flag=0;

    bool hasPathSum(TreeNode *root, int sum) {
        if(root==NULL) return false;
        
        pathSum(root,0,sum);
        
        if(flag==1)
            return true;
        else
            return false;
        
    }
    
    int pathSum(TreeNode *root,int res,int sum)
    {
        if(root==NULL)  return 0;
        
        res+=root->val;
        
        int l=pathSum(root->left,res,sum);
        int r=pathSum(root->right,res,sum);
        
        if((l+r)==0&&res==sum)
        {
            flag=1;
        }
        
    }
};