470. 用 Rand7() 实现 Rand10()

470. 用 Rand7() 实现 Rand10()

挺有趣的
先把代码放上来，明天重新推一遍理论再放上来

class Solution {
public:
    int rand10() {
        while(true) {
            int a = rand7(), b = rand7();
            int res = (a - 1) * 7 + b;
            if (res <= 40) return res % 10 + 1;
            
            a = res - 40, b = rand7();
            res = (a - 1) * 7 + b;
            if (res <= 60) return res % 10 + 1;

            a = res - 60, b = rand7();
            res = (a - 1) * 7 + b;
            if (res <= 20) return res % 10 + 1;
        }
    }
};