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.

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.

Analysis

``````root.val == sum && root.left == null && root.right == null
``````

``````hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val)
``````

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;
}
if (root.val == sum && root.left == null && root.right == null) {
return true;
}
return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
}
}
``````