Method integerBreak

343. Integer Break/Solution.cpp:17–27

2 <= n <= 58

public:
    // 2 <= n <= 58 
    int integerBreak(int n) {
        if (n == 2) return 1;
        if (n == 3) return 2;
        if (n == 4) return 4;
        int n3 = 0;
        while (n >= 5) {
            n3 ++ ;
            n -= 3;
        }
        return fast_pow(3, n3) * n;
    }

    int fast_pow(int x, int y) {
        int res = 1;