leetcode解题之374. Guess Number Higher or Lower Java版 (猜数字大小二分查找）

374. Guess Number Higher or Lower

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.

/* The guess API is defined in the parent class GuessGame.
@param num, your guess
@return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num); */
//二分查找猜测数字大小
public class Solution extends GuessGame {
public int guessNumber(int n) {
int start = 1;
int end = n;
while (start <= end) {
// mid = (low + high) / 2;会溢出
int mid = start + (end - start) / 2;
int res = guess(mid);
if (res == 0)
return mid;
else if (res == 1) {
start = mid + 1;
} else {
end = mid - 1;
}
}
return start;

}
}