【leetcode】374. Guess the size of the number

subject :

374.  Guess the size of the numbers 
 The rules of the number guessing game are as follows ：
 Every round of the game , I'll start from  1  To  n  Randomly choose a number .  Please guess which number is chosen .
 If you guessed wrong , I'll tell you , Is your guess larger or smaller than the number I selected .
 You can call a predefined interface  int guess(int num)  To get a guess , The total number of return values is  3  A possible situation （-1,1  or  0）：

-1： The number I picked is smaller than your guess  pick < num
1： The number I picked was bigger than you guessed  pick > num
0： I picked the same number as you guessed . Congratulations ！ You guessed it ！pick == num
 Back to the number 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
 Example  4：

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

1 <= n <= 231 - 1
1 <= pick <= n

Dichotomy ：

/** * Forward declaration of guess API. * @param num your guess * @return -1 if num is lower than the guess number * 1 if num is higher than the guess number * otherwise return 0 * int guess(int num); */
public class Solution extends GuessGame {
    
    public int guessNumber(int n) {
    
        int left = 1;
        int right = n;
        while(true){
    
            int mid = (right - left) / 2 + left;
            int ans = guess(mid);
            if(ans == 1) left = mid + 1;
            else if(ans == -1) right = mid;
            else {
    return mid;}
        }
    }
}