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.
Follow up:
- What is the expected value for the number of calls to
rand7() function? - Could you minimize the number of calls to
rand7()?
class Solution extends SolBase {
public int rand10() {
int i,j;
while( (i = rand7()) > 6); // P(i is even) = P(i is odd) = 0.5
while( (j = rand7()) > 5); // P(j==1) = P(j==2) = P(j==3) = P(j==4) = P(j==5) = 0.2
return i % 2 == 0 ? j : j + 5;
}
}阴间方法？？居然是brain teaser
想一下要random get 1-10，给的条件只有random get 1-7，怎么办？
上面的方法是平等的拿到奇偶数(如果i是7就继续循环，反正得到1-6就可以了，而123456奇偶概率相等)，然后再平等的拿到1-5（如果j是6，7就循环，直到得到12345（概率相等）就停止），然后如果even和odd各返回1-5 和 6-10 屮
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