112. Path Sum

keyword: root to leaf

time: O(n)

space: O(n)

class Solution {
    public boolean hasPathSum(TreeNode root, int targetSum) {
        if (root == null) return false;
        if (root.left == null && root.right == null) {
            return targetSum == root.val;
        }
        return hasPathSum(root.left, targetSum - root.val) || 
        hasPathSum(root.right, targetSum - root.val);
    }
}