470. Implement Rand10() Using Rand7()

class Solution extends SolBase {
    public int rand10() {
        while (true) {
            int random = (rand7() - 1) * 7 + (rand7() - 1); // [0, 6] * 7 + [0, 6] -> [0, 48]
            if (random >= 0 && random <= 39) {
                return random % 10 + 1; // 注意结果要求返回 [1, 10] 范围中的数字，所以此处加 1
            }
        }
    }
}

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