174C - Range Increments - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;
int n,s;
stack<int> l,r;
int main()
{
    cin>>n;
    int a[n+1];
  	for (int i=0;i<n;i++)cin>>a[i]; 
    a[n]=0;
    for(int i=0;i<=n;i+=1){
    while(s<a[i])l.push(i+1),s++;
    while(s>a[i])r.push(i),s--;
    }
    cout<<l.size()<<'\n';
  	while (l.size()) cout<<l.top()<<' '<<r.top()<<'\n',l.pop(),r.pop();
    
}/*1691140156.3667114*/