374. Guess Number Higher or Lower

题目描述

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.

二分法

# The guess API is already defined for you.
# @param num, your guess
# @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
# def guess(num):

class Solution(object):
    def guessNumber(self, n):
        """
        :type n: int
        :rtype: int
        """
        low = 1
        high = n
        while low <= high:
            mid = (low + high) // 2
            res = guess(mid)
            if res == 0:
                return mid
            elif res == -1:
                high = mid - 1
            else:
                low = mid + 1

三分法

/* 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) {
        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 -1;
    }
}