# LeetCode 374. Guess Number Higher or Lower
[374. Guess Number Higher or Lower](leetcode_url) (難度 通過率)
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(<font color=#00AF9B>Easy</font> 53.8%)
(<font color=#FFB800>Medium</font> 39.6%)
(<font color=#FF375F>Hard</font>)
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- 限制 :

<ul>
<li><code>1 <= n <= 2³¹ - 1</code></li>
<li><code>1 <= pick <= n</code></li>
</ul>

- Solution
沒特別變化的 binary search。
- 時間複雜度: $O(lg(n))$
- 空間複雜度: $O(1)$

- 程式碼

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

    class Solution {
    public:
        int guessNumber(int n) {
            int min_index = 0, max_index = n;
            while(min_index <= max_index)
            {
                int mid_index = (max_index - min_index) / 2 + min_index;
                if(guess(mid_index) == 0) return mid_index;
                if(guess(mid_index) == 1) min_index = mid_index + 1;
                if(guess(mid_index) == -1) max_index = mid_index - 1;
            }
            return -1;
        }
    };

</details>