129. Sum Root to Leaf Numbers

LC120Solution.swift

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func sumNumbers(_ root: TreeNode?) -> Int {
        if root == nil { return 0 }
        var sum = [0]
        sumRootToLeft(root, cur: 0, sum: &sum)
        return sum[0]
    }

    func sumRootToLeft(_ root: TreeNode?, cur: Int, sum: inout [Int]) {
        if (root == nil) { return }
        if root!.left == nil && root!.right == nil {
            let curNum = cur * 10 + root!.val
            sum[0] += curNum
            return
        }
        if root!.left != nil {
            sumRootToLeft(root!.left, cur: cur * 10 + root!.val, sum: &sum)
        }
        if root!.right != nil {
            sumRootToLeft(root!.right, cur: cur * 10 + root!.val, sum: &sum)
        }
    }
}