题目：

题解：

class Solution extends SolBase {public int rand10() {int a, b, idx;while (true) {a = rand7();b = rand7();idx = b + (a - 1) * 7;if (idx <= 40) {return 1 + (idx - 1) % 10;}a = idx - 40;b = rand7();// get uniform dist from 1 - 63idx = b + (a - 1) * 7;if (idx <= 60) {return 1 + (idx - 1) % 10;}a = idx - 60;b = rand7();// get uniform dist from 1 - 21idx = b + (a - 1) * 7;if (idx <= 20) {return 1 + (idx - 1) % 10;}}}
}