470. Implement Rand10() Using Rand7()

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.

Do NOT use system's Math.random().

Example 1:

Input: 1
Output: [7]

Example 2:

Input: 2
Output: [8,4]

Example 3:

Input: 3
Output: [8,1,10]

Note:

    rand7 is predefined.
    Each testcase has one argument: n, the number of times that rand10 is called.

Give up illegal data points

class Solution extends SolBase {
    public int rand10() {
        int row = 0, col = 0, index = 41;
        while(index > 40) {
            row = rand7();
            col = rand7();
            index = col + (row - 1) * 7;
        }
        return 1 + (index - 1) % 10;
    }
}