smallest subsequence that contains all integers from 1 to given number(sliding window technique)

 /// Its Work For Positive Number(Greater Than Zero)

#include<bits/stdc++.h>

#define N 1000000

using namespace std;

int position[N], preposition[N];

bool flag[N];

int main()

{

int n, value;

cout << "Enter Array Size :: ";

cin >> n;

int a[n];

cout << "\nEnter Array Element :: ";

for(int i=0;i<n;i++)

cin >> a[i];

cout << "\n";

cout << "Enter A Number :: ";    /// 1 to value that subsequence search in this array

cin >> value;

for(int i=0;i<N;i++)

position[i] = -1;

for(int i=n-1;i>=0;i--)

{

preposition[i] = position[a[i]];

position[a[i]] = i;

}

int cnt = 0, left = 0, right = -1;

for(int i=0;i<N;i++)

flag[i] = false;

for(int i=0;i<n;i++)

{

if(a[i] <= value && flag[a[i]] == false)

{

flag[a[i]] = true;

cnt++;

}

if(cnt == value)

{

right = i;

break;

}

}

if(right == -1)

{

cout << "Smallest Sequence Not Found." << "\n";

return 0;

}

int minimum = right - left + 1;

while(left < right)

{

if(a[left] > value)

left++;

else if(preposition[left] == -1)

break;

else if(preposition[left] <= right)

left++;

else

{

right = preposition[left];

left++;

}

minimum = min(minimum, (right-left+1));

}

cout << "\nSmallest Subsequence Length :: " << minimum << "\n";

return 0;

}