374 Guess Number Higher or Lower
1. Question
We are playing the Guess Game. The game is as follows:
I pick a number from1ton. 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 APIguess(int num)
which returns 3 possible results (-1
,1
, or0
):
-1 : My number is lower
1 : My number is higher
0 : Congrats! You got it!
Example:
n = 10, I pick 6.
Return 6.
2. Implementation
(1) Binary Search
/* 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); */
public class Solution extends GuessGame {
public int guessNumber(int n) {
int start = 1, end = n, mid = 0;
while (start <= end) {
mid = start + (end - start) / 2;
if (guess(mid) == -1) {
end = mid - 1;
}
else if (guess(mid) == 1) {
start = mid + 1;
}
else {
return mid;
}
}
return -1;
}
}
3. Time & Space Complexity
时间复杂度O(logn), 空间复杂度O(1)
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