2017-08-31 15:51:42 +0000   |     algorithm leetcode binary search   |   Viewed times   |    

题目

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.

标准二分查找,

代码

/* The guess API is defined in the parent class GuessGame.
 * @param num, your guess
 * @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
 * int guess(int num);
 */
public class Solution extends GuessGame {
    public int guessNumber(int n) {
        return helper(1,n);
    }
    private int helper(int lo, int hi) {
        if (lo >= hi) { return lo; }
        int mid = lo + (hi - lo) / 2;
        int answer = guess(mid);
        switch (answer) {
            case 1: return helper(mid+1,hi);      // mid too small
            case -1: return helper(lo,mid-1);     // mid too big
            case 0: return mid;                   // BINGO
            default: return 0;
        }
    }
}

结果

guess-number-higher-or-lower-1