LeetCode – Refresh – Find Peak Element

The ticky part for this question is :

mid == 0     num[mid] < num[mid+1]   start = mid + 1;

0 < mid < len num[mid-1] < num[mid] < num[mid+1] start = mid + 1;

0 < mid < len num[mid-1] > num[mid] > num[mid+1] end = mid - 1;

mid = l num[mid] < num[mid-1] end = mid - 1;

 

But after we do the comparison, we can simplify the condition:

mid == 0 ||  mid < length-1 && num[mid] < num[mid + 1]   start = mid + 1

mid == length-1 || mid > 0 && num[mid] > num[mid - 1] end = mid - 1

 

class Solution {
public:
    int findPeakElement(const vector<int> &num) {
        int start = 0, end = num.size()-1, mid = 0;
        while (start <= end) {
            mid = (start + end)/2;
            if ((mid == 0 || num[mid] > num[mid-1]) &&
                (mid == num.size()-1 || num[mid] > num[mid+1])) {
                return mid;
            } else if (mid == 0 || (mid < num.size()-1 && num[mid] < num[mid+1])){
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }
    }
};