22. Generate Parentheses

22. Generate Parentheses.swift

class Solution {
    func generateParenthesis(_ n: Int) -> [String] {
        var result = [String]()
        if(n == 0) {
            return result
        }
        var str = ""
        generateParenthesisUtil(&result,str,n,0,0)
        return result
    }
    
    func generateParenthesisUtil(_ result:inout [String],_ str: String, _ n:Int, _ left:Int, _ right:Int) {
        if right == n {
            result.append(str)
            return
        }
        if (left < n) {
            let s = str + "("
            generateParenthesisUtil(&result,s, n, left + 1, right)
        }
        if(left > right) {
            let s = str + ")"
            generateParenthesisUtil(&result,s, n, left, right + 1)
        }
    }
}