Index Sort

/************************************************************************/
/* given an array of integer, 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
eg. input: 1,2,4,7,10,11,12,7,12,6,7,16,18,19
output: (3,10)*/

/* basic idea: using two stacks to remember the numbers, one is from head and the
other is from the tail. */
/************************************************************************/

#include <iostream>
#include <stack>

using namespace std;

int getindiceFhead(int a[], int length);
int getindiceFtail(int a[], int length);

void getIndices(int a[], int length) {

       int m, n;
       m = getindiceFhead(a, length);
       n = getindiceFtail(a, length) - m;

       cout<< "("<<m<<", "<<n<<")"<<endl;
}

int getindiceFhead(int a[], int length) {
       stack<int> head;
       int flag = 0;
       head.push(a[0]);
       for (int i = 1; i < length; i++)
       {
              if (a[i] >= head.top() && flag == 0)
              {
                     head.push(a[i]);
              }
              while(a[i] < head.top() && head.size() > 1) {
                     flag = 1;
                     head.pop();
              }
       }
       return head.size();
}

int getindiceFtail(int a[], int length) {
       stack<int> tail;
       int flag = 0;

       tail.push(a[length-1]);

       for(int i = length-2; i >= 0; i--) {
              if (a[i] <= tail.top() && flag == 0)
              {
                     tail.push(a[i]);
              }
              while(a[i] > tail.top() && tail.size() > 1) {
                     flag = 1;
                     tail.pop();
              }
       }

       return length-tail.size();
}



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