【Leetcode】374. Guess Number Higher or Lower【二分搜索】

374. Guess Number Higher or Lower

Total Accepted: 17904
Total Submissions: 56954
Difficulty: Easy

We are playing the Guess Game. The game is as follows:

I pick a number from 1 to n. You have to guess which number I picked.

Every time you guess wrong, I'll tell you whether the number is higher or lower.

You call a pre-defined API

guess(int num)

which returns 3 possible results (

-1

,

1

, or

0

):

-1 : My number is lower
1 : My number is higher
0 : Congrats! You got it!

Example:

n = 10, I pick 6.

Return 6.

思路：二分法

代码1：

public class Solution extends GuessGame {
public int guessNumber(int n) {
int begin = 1, end = n, mid;
while(begin <= end){
mid = begin + (end - begin)/2;
int flag = guess(mid);
if(flag == 0) return mid;
if(flag < 0) end = mid - 1;
else begin = mid + 1;
}
return begin;
}
}

代码2：http://blog.csdn.net/corpsepiges/article/details/51898386

public class Solution extends GuessGame {
public int guessNumber(int n) {
return guessRange(1,n);
}
public int guessRange(int start,int end){
if(start==end){
return start;
}
int middle=start/2+end/2+(start%2+end%2)/2;
int ans=guess(middle);
if(ans==0){
return middle;
}
if(ans>0){
return guessRange(middle+1,end);
}
return guessRange(start,middle-1);
}
}