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.
猜数字,返回-1,往更小的猜,返回1往更大的猜
int mid = (left+right)>>1 会溢出
C++(3ms):
1 // Forward declaration of guess API. 2 // @param num, your guess 3 // @return -1 if my number is lower, 1 if my number is higher, otherwise return 0 4 int guess(int num); 5 6 class Solution { 7 public: 8 int guessNumber(int n) { 9 int left = 1 ; 10 int right = n ; 11 while(left <= right){ 12 int mid = left + (right - left)/2 ; 13 int t = guess(mid) ; 14 if (t == 0) 15 return mid ; 16 else if (t == -1) 17 right = mid - 1; 18 else if (t == 1) 19 left = mid + 1 ; 20 } 21 } 22 };