112.path-sum.kt

/*
 * @lc app=leetcode id=112 lang=kotlin
 *
 * [112] Path Sum
 *
 * https://leetcode.com/problems/path-sum/description/
 *
 * algorithms
 * Easy (38.47%)
 * Likes:    1093
 * Dislikes: 358
 * Total Accepted:    345.6K
 * Total Submissions: 896.5K
 * Testcase Example:  '[5,4,8,11,null,13,4,7,2,null,null,null,1]\n22'
 *
 * 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.
 * 
 */
/**
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    private var ans: Int = 0
    fun hasPathSum(root: TreeNode?, sum: Int): Boolean {
        if (root == null) return false
        val cnt = sum-root!!.`val`
        if (root?.left == null && root?.right == null && cnt == 0)
            return true
        return hasPathSum(root?.left, cnt) ||
            hasPathSum(root?.right, cnt)
    }

}