[LeetCode] Find Minimum in Rotated Sorted Array

Suppose a sorted array is rotated at some pivot unknown to you beforehand.

(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

Find the minimum element.

You may assume no duplicate exists in the array.

class Solution {
public:
    int findMinHelper(vector<int> &num, int left, int right) {
        int mid = (left + right) / 2;
        if (mid == left || mid == right) return min(num[left], num[right]);
        if (num[mid] < num[right]) {
            return findMinHelper(num, left, mid);
        } else {
            return findMinHelper(num, mid, right);
        }
    }
    
    int findMin(vector<int> &num) {
        return findMinHelper(num, 0, num.size() - 1);
    }
};

二分查找，注意边界情况的判断。用中间元素与最左边元素比较。只有两种情况，最小值要么在最左边，要么在最右边。二分时要保留中间元素，以防止最小值就是中间的元素。