Guess Number Higher or Lower

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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 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:

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Input: n = 10, pick = 6
Output: 6

Example 2:

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Input: n = 1, pick = 1
Output: 1

Example 3:

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Input: n = 2, pick = 1
Output: 1

二分法：

时间复杂度：O(logn)

空间复杂度：O(1)

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class Solution {
public:
    int guessNumber(int n) {
        int left = 0;
        int right = n;
        while(1) {
            int mid = left + (right - left)/2;
            if(guess(mid) == 1)left = mid + 1;
            else if(guess(mid) == -1) right = mid;
            else return mid;
        }

    }
};