585.maximum-number-in-mountain-sequence.cpp

//  Tag: Binary Search
//  Time: O(logN)
//  Space: O(1)
//  Ref: -
//  Note: -

//  Given a mountain sequence of `n` integers which increase firstly and then decrease, find the mountain top(Maximum).
//  
//  ---
//   
//  
//  Example 1:
//  ```
//  Input: nums = [1, 2, 4, 8, 6, 3] 
//  Output: 8
//  ```
//  Example 2:
//  ```
//  Input: nums = [10, 9, 8, 7], 
//  Output: 10
//  ```
//  
//  Arrays are strictly incremented, strictly decreasing

class Solution {
public:
    /**
     * @param nums: a mountain sequence which increase firstly and then decrease
     * @return: then mountain top
     */
    int mountainSequence(vector<int> &nums) {
        // write your code here
        int n = nums.size();
        int left = 0;
        int right = n - 1;
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] < nums[mid + 1]) {
                left = mid + 1;
            } else {
                right = mid;
            }
        }

        return nums[left];
    }
};