解题思路:
由于数量级较大,需要使用long以及快速幂求余
下图便于理解快速幂求余
class Solution {public int cuttingBamboo(int bamboo_len) {if(bamboo_len <= 3) return bamboo_len - 1;int b = bamboo_len % 3, p = 1000000007;long rem = 1, x = 3;for(int a = bamboo_len / 3 - 1; a > 0; a /= 2) {//a减一是为了少切分一个3,留给后面b的取值讨论if(a % 2 == 1) rem = (rem * x) % p;x = (x * x) % p;}if(b == 0) return (int)(rem * 3 % p);if(b == 1) return (int)(rem * 4 % p);return (int)(rem * 3 * 2 % p);}
}