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Leetcode 112 Path Sum.

Leetcode 112 Path Sum

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.


It is not a hard problem, but I spend a lot of time on it.

It is really confusing for me about the "return", my original code have two returns, then if I add a return for the whole system, every time the program execute to that line, it will return a false. Will not do the rest any more.


/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if(root==null ){
           return false;
        }

        if(root.val==sum && root.left==null && root.right==null){
            return true;
        }
        if(root!=null && root.left!=null){
            root.left.val=(root.val+root.left.val);
        }
        if(root!=null && root.right!=null){
            root.right.val=(root.val+root.right.val);
        }

            return hasPathSum(root.left,sum)||hasPathSum(root.right,sum);



    }
}
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