L112. Path Sum

recursion

Problem:

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:

• input - each node, if it is 0, return true

public boolean pathSum(TreeNode root, int sum){
    if(root == null) return false;
    if(root.left == null && root.right == null){
        return sum - root.val == 0;
    }
    return pathSum(root.left, sum - root.val) || pathSum(root.right, sum - root.val);
}