面试题 14- II. 剪绳子 II

输入: 2
输出: 1
解释: 2 = 1 + 1, 1 × 1 = 1

输入: 10
输出: 36
解释: 10 = 3 + 3 + 4, 3 × 3 × 4 = 36

class Solution:
    def cuttingRope(self, n: int) -> int:
        if n < 4:
            return n - 1
        res = 1
        while n > 4:
            res *= 3
            n -= 3
        if n == 4:
            return (res << 2) % 1000000007
        return (res * n) % 1000000007

class Solution {
    public int cuttingRope(int n) {
        if (n < 4) {
            return n - 1;
        }
        int s1 = n / 3;
        int m = n % 3;
        if (m == 1) {
            s1 -= 1;
            m = 4;
        }
        long res = 1;
        while (s1-- > 0) {
            res *= 3;
            res %= 1000000007;
        }
        return (int) ((res * (m == 0 ? 1 : m)) % 1000000007);
    }
}

/**
 * @param {number} n
 * @return {number}
 */
var cuttingRope = function (n) {
  if (n <= 3) return n - 1;
  let a = ~~(n / 3);
  let b = n % 3;
  const MOD = 1e9 + 7;
  function myPow(x) {
    let r = 1;
    for (let i = 0; i < x; i++) {
      r = (r * 3) % MOD;
    }
    return r;
  }
  if (b === 1) {
    return (myPow(a - 1) * 4) % MOD;
  }
  if (b === 0) return myPow(a) % MOD;
  return (myPow(a) * 2) % MOD;
};

func cuttingRope(n int) int {
	if n <= 3 {
		return n - 1
	}
	sum := 1
	for n > 4 {
		sum *= 3
		sum = sum % 1000000007
		n -= 3
	}
	return sum * n % 1000000007
}

class Solution {
public:
    int cuttingRope(int n) {
        const int mod = 1000000007;
        if (n < 4) return n - 1;
        long long ans = 1;
        while (n > 4) {
            ans = ans * 3 % mod;
            n -= 3;
        }
        if (n == 4)
            return ans * 4 % mod;
        return ans * n % mod;
    }
};