Guess Number Higher or Lower(leetcode374)

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 :

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

solutions：

//所有查一遍 除了效率不行 仍是能完成任務的
public static int guessNumber(int n) {
       for (int i =1;i<=n;i++){
           if(guess(i)==0){
               return i;
           }
       }
       return Integer.MIN_VALUE;
}

 

//二分查找
    public static int guessNumber2(int n) {

        int low = 1;
        int high = n;
        while(low <= high){

            int mid = low + (high - low) / 2;
            //這種寫法可能會溢出
//            int mid =  (high + low) / 2;
            int guess = guess(mid);
            if(guess == 0){
                return mid;
            }
            if(guess < 0){
                high = mid -1;
            }
            if(guess > 0){
                low = mid+1;
            }

        }
        return Integer.MIN_VALUE;
    }

 

//看到其餘的solution 寫了三分搜索 和二分實際上是差很少的
public static int guessNumber3(int n) {
    int low = 1;
    int high = n;
    while (low <= high) {
        int mid1 = low + (high - low) / 3;
        int mid2 = high - (high - low) / 3;
        int res1 = guess(mid1);
        int res2 = guess(mid2);
        if (res1 == 0) {
            return mid1;
        }
        if (res2 == 0) {
            return mid2;
        } else if (res1 < 0) {
            high = mid1 - 1;
        } else if (res2 > 0) {
            low = mid2 + 1;
        } else {
            low = mid1 + 1;
            high = mid2 - 1;
        }
    }
    return Integer.MIN_VALUE;
}

git：https://github.com/woshiyexinjie/leetcode-xin