find unsorted subarray

/* 19-6 Given an array of integers. write a method to find indices m and n such that

   if you sorted elements m through n, the entire array would be sorted.

   Minimize n - m (that is, find the smallest such sequence). */

const int EMPTY_ARRAY = -2;

const int SORTED_ARRAY = -1;

pair<int,int> findUnsortedIndices(int [], int);

int findFirstUnsortedIndex(int [], int);

int findLastUnsortedIndex(int [], int);

pair<int,int> findUnsortedIndices(int arr[], int len){

    pair<int,int> indices;

    indices.first = findFirstUnsortedIndex(arr, len);

    indices.second = findLastUnsortedIndex(arr, len);

    return indices;

}

int findFirstUnsortedIndex(int arr[], int len){

    if (len == 0) {

        return EMPTY_ARRAY;

    }

    if (len == 1) {

        return SORTED_ARRAY;

    }

    stack<int> s;

    bool elementsInOrder = true;

    s.push(arr[0]);

    for (int i = 1; i < len; i++) {

        if (arr[i] >= s.top() && elementsInOrder) {

            s.push(arr[i]);

        } else {

            elementsInOrder = false;

            while (arr[i] < s.top()) {

                s.pop();

            }

        }

    }

    if ((int)s.size() == len) {

        return SORTED_ARRAY;

    }

    return (int)s.size();

}

int findLastUnsortedIndex(int arr[], int len){

    if (len == 0) {

        return EMPTY_ARRAY;

    }

    if (len == 1) {

        return SORTED_ARRAY;

    }

    stack<int> s;

    bool elementsInOrder = true;

    s.push(arr[len-1]);

    for (int i = len-2; i >= 0; i--) {

        if (arr[i] <= s.top() && elementsInOrder) {

            s.push(arr[i]);

        } else {

            elementsInOrder = false;

            while (arr[i] > s.top()) {

                s.pop();

            }

        }

    }

    if ((int)s.size() == len) {

        return SORTED_ARRAY;

    }

    return len - 1 - (int)s.size();

}