16. 3Sum Closest

    func threeSumClosest(_ nums: [Int], _ target: Int) -> Int {
        guard nums.count > 2 else{ return  0}
        let sorted = nums.sorted()
        var res:Int?

        for i in 0 ... sorted.count - 3 {
            var p1 = i + 1
            var p2 = sorted.count - 1
            while p1 < p2{
                let cur = sorted[p1] + sorted[p2] + sorted[i]
                if  res == nil || abs( target - res!) > abs( target - cur) { res = cur }
                if cur == target {
                    return target
                }else if cur < target {
                    p1 += 1
                }else {
                    p2 -= 1
                }
            }
        }
        return res!
    }