Path Sum

iven 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.

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.

Return 0 / 1 ( 0 for false, 1 for true ) for this problem

Method:

DFS

Solution:

Time: O(n)
Space: O(1)

/**
 * Definition for binary tree
 * class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) {
 *      val = x;
 *      left=null;
 *      right=null;
 *     }
 * }
 */
public class Solution {
    public int hasPathSum(TreeNode A, int B) {
        if (A == null) return 0;
        if (A.left == null && A.right == null) {
            return A.val == B ? 1 : 0;
        }
        if (A.left == null) {
            return hasPathSum(A.right, B - A.val);
        }
        if (A.right == null) {
            return hasPathSum(A.left, B - A.val);
        }
        int left = hasPathSum(A.left, B - A.val);
        int right = hasPathSum(A.right, B - A.val);
        return Math.max(left, right);
    }
}