Leetcode112-pathSum

Description

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.

Note: A leaf is a node with no children.

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.

Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean hasPathSum(TreeNode root, int sum) {
        if (root == null) return false;
        return dfs(root, sum, 0);
    }
    private boolean dfs(TreeNode node, int sum, int cur){
        if (node == null) return false;
        cur += node.val;
        if (node.left == null && node.right == null){
            if (cur == sum) return true;
            return false;
        }
        return dfs(node.left, sum, cur) || dfs(node.right, sum, cur);
    }
}

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