[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.

Analysis:

Since it is sorted array, binary search may be the hint. Let m be the middle index of array num, if num[0] < num[m], then first part is sorted, the minimum element would be either num[0] or the minimum of the second part, which can be computed recursively. Similarly, if num[m] < num[n], second part is sorted, the minimum element would be either num[m] or the minimum of the first part. 

 int findMin(vector<int> &num) {
        int b = 0;
        int e = num.size() - 1;
        int minValue = INT_MAX;
        while(b <= e) {
            int m = b + (e- b)/2;
            //it is sorted from b to m
            if (num[b] <= num[m]) {
                minValue = min(num[b], minValue);
                b = m + 1;
            }
            else {
                minValue = min(num[m], minValue);
                e = m-1;
            }
        }
        return minValue;
    }