Maximum Unsorted Subarray

• Time : $O(n)$
• Space : $O(1)$

vector<int> Solution::subUnsort(vector<int> &A) {
    int n = A.size(), l = n, r = -1;
    for(int i = 0; i < n; i++) {
        if(i and A[i] < A[i - 1]) {
            l = min(l, i - 1);
            r = max(r, i);
            while(l >= 0 and A[l] > A[i]) l--;
        }
        if(i + 1 < n and A[i] > A[i + 1]) {
            l = min(l, i);
            r = max(r, i + 1);
            while(r < n and A[r] < A[i]) r++;
        }
    }
    
    if(l == n) return {-1};
    return {l + 1, r - 1};
}