[E二分] lc374. 猜数字大小(二分+水题)

Posted 2021-07-28 Ypuyu

文章目录

• • 1. 题目来源
  • 2. 题目解析

1. 题目来源

链接：374. 猜数字大小

2. 题目解析

水题，二分。

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时间复杂度：$O(logn)$

空间复杂度：$O(1)$

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

class Solution {
public:
    int guessNumber(int n) {
        int l = 1, r = n;
        while (l < r) {
            int mid = 0ll + l + r + 1 >> 1;
            //if (guess(mid) == 0) return mid;      // 可有可无

            if (guess(mid) == -1) r = mid - 1;
            else l = mid;
        }

        return l;
    }
};