題目：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.

猜數(shù)字，給一個范圍［1，n］，猜了以后用 guess(int num)告訴是猜對，還是猜大／小了。

二分查找。

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int low = 1, high = n;
        int pick = low + (high - low) / 2;
        while(low <= high && guess(pick) != 0){
            if (guess(pick) == 1) low = pick +1;
            else high = pick -1;
            pick = low + (high - low) / 2;
        }
        return pick;
        
    }
}

減少調(diào)用guess（num）的次數(shù)，return那里返回low或high都可以，因為跳出循環(huán)的時候，low＝high。

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int low = 1, high = n;
        int pick;
        int tip;
        while(low < high){
            pick = low + (high - low) / 2;
            tip = guess(pick);
            if(tip == 0) return pick;
            else if (tip == 1) low = pick + 1;
            else high = pick - 1;
           
        }
        return high;//or low
        
    }
}