[Swift]LeetCode372. 超级次方 | Super Pow

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➤微信公众号：山青咏芝（shanqingyongzhi）
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Your task is to calculate ab mod 1337 where a is a positive integer and bis an extremely large positive integer given in the form of an array.

Example 1:

Input: a = 2, b = [3]
Output: 8

Example 2:

Input: a = 2, b = [1,0]
Output: 1024

---

你的任务是计算 ab 对 1337 取模，a 是一个正整数，b 是一个非常大的正整数且会以数组形式给出。

示例 1:

输入: a = 2, b = [3]
输出: 8

示例 2:

输入: a = 2, b = [1,0]
输出: 1024

---

68ms

class Solution {
    let mod = 1337
    func superPow(_ a: Int, _ b: [Int]) -> Int {
        guard b.count > 0 else {
            return 1
        }
        var num = 1
        var tmpA = a
        for tmpNum in b.reversed() {
            num = powMod(tmpA, tmpNum) * num % mod
            tmpA = powMod(tmpA, 10);
        }
        return num
    }
    
    private func powMod(_ a: Int, _ m: Int) -> Int{
        let tmpA = a % mod
        var result = 1
        for _ in 0 ..< m {
            result = result * tmpA % mod
        }
        return result
    }
}

---

76ms

class Solution {
    func superPow(_ a: Int, _ b: [Int]) -> Int {
        var rst: Int = 1;
        var x = a;
        for n in b {
            rst = newPow(rst, 10) * newPow(x, n) % 1337;
        }
        return rst;
    }
    
    func newPow(_ x: Int, _ n: Int) -> Int {
        if n == 0{
            return 1;
        }
        if n == 1{
            return x % 1337;
        }
        
        return newPow(x % 1337, n / 2) * newPow(x % 1337, n - n / 2) % 1337;
    }
}

---

108ms

class Solution {
    func superPow(_ a: Int, _ b: [Int]) -> Int {
        
        var result:Int=1
        
        for i in 0...b.count-1 {
            result = self.pow(result, 10) * pow(a, b[i]) % 1337
        }
        
        return result;
    }
    func pow(_ x: Int ,_ n: Int) -> Int {
        if (n == 0) {return 1}
        if (n == 1) {return x % 1337}
        return pow(x % 1337, n / 2) * pow(x % 1337, n - n / 2) % 1337;

    }
}

---

 168ms

class Solution {
    func superPow(_ a: Int, _ b: [Int]) -> Int {
        var res:Int = 1
        for i in 0..<b.count
        {
            res = pow(res, 10) * pow(a, b[i]) % 1337
        }
        return res
    }
    
    func pow(_ x:Int,_ n:Int) -> Int
    {
        if n == 0 {return 1}
        if n == 1 {return x % 1337}
        return pow(x % 1337, n / 2) * pow(x % 1337, n - n / 2) % 1337
    }
}