# Why my binary search get time limit exceed error

• Here is my JAVA solution, but get time limit exceed error

``````public class Solution extends GuessGame {
public int guessNumber(int n) {
int begin = 0;
int end = n + 1;
int start;
while(true){
start = (begin + end) / 2;
int result = guess(start);
if(result == 0) return start;
if(result < 0) end = start;
else begin = start;
}
}
}
``````

• i find that the begin+end will overflow and turn out to be a negative number, when input n is very big. So I change start = begin + (end - begin)/2.

• @bargitta The test cases include the MAX_Integer 2147483647, which means 2147483647 + 1 will turn out to be a negative value. Thus I should not use end = n + 1 or begin+end.

Here is the right one

`````` int begin = 1;
int end = n;
int start;
while(true){
start = begin + (end - begin) / 2;
int result = guess(start);
if(result == 0) return start;
if(result < 0) end = start - 1;
else begin = start + 1;
}

``````

• @bargitta That seems to be the correct reason. We should use (max-min)/2+min from now on to evade the possible problem.

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