[leetcode]470. Implement Rand10() Using Rand7()

Analysis

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Given a function rand7 which generates a uniform random integer in the range 1 to 7, write a function rand10 which generates a uniform random integer in the range 1 to 10.

利用rand7()生成一個randM() (此處M是10的整數)

Implement

// The rand7() API is already defined for you.
// int rand7();
// @return a random integer in the range 1 to 7

class Solution {
public:
    int rand10() {
        int num = rand40();
        return num%10+1;
    }
private:
    int rand49(){
        int num = 7*(rand7()-1)+rand7()-1;
        return
 
 num;
    }
    int rand40(){
        int num = rand49();
        while(num >= 40)
            num = rand49();
        return num;
    }
};