374. Guess Number Higher or Lower

Tags: Bianry Search Easy

Company: Google

Links: https://leetcode.com/problems/guess-number-higher-or-lower/

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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

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// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);

class Solution {
public:
    int guessNumber(int n) {
        int left = 0, right = n;
        int pick = left + ((right - left) >> 1);
        int flag = guess(pick);

        if (flag != 0) {
            do {
                if (flag == 1){
                    left = pick + 1;
                    pick = left + ((right - left) >> 1);
                    flag = guess(pick);
                } 
                else if (flag == -1) {
                    right = pick - 1;
                    pick = left + ((right - left) >> 1);
                    flag = guess(pick);
                }
            } while (flag != 0);
        }

        return pick;
    }
};