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 will tell you whether the number I picked is higher or lower than your guess.
You call a pre-defined API int guess(int num), which returns three possible results:
-1: Your guess is higher than the number I picked (i.e. num > pick).
1: Your guess is lower than the number I picked (i.e. num < pick).
0: your guess is equal to the number I picked (i.e. num == pick).
Return the number that I picked.
Example 1:
Input: n = 10, pick = 6
Output: 6
Example 2:
Input: n = 1, pick = 1
Output: 1
Example 3:
Input: n = 2, pick = 1
Output: 1
Constraints:
1 <= n <= 231 - 1
1 <= pick <= n
思路一：二分法
public int guessNumber(int n) {
int low = 1;
int high = n;
while (low <= high) {
int mid = low + (high - low) / 2;
int test = guess(mid);
if (test == -1) {
high = mid - 1;
} else if (test == 1) {
low = mid + 1;
} else {
return mid;
}
}
throw new RuntimeException();
}