cf Sereja and Array

http://codeforces.com/contest/315/problem/B

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define maxn 200000
using namespace std;

int a[maxn],b[maxn],c,v,x;

int main()
{
    int n,m;
    cin>>n>>m;
    for(int i=0; i<n; i++)
    {
        cin>>a[i];
    }
    int ans=0;
    for(int i=0; i<m; i++)
    {
        cin>>c;
        if(c==1)
        {
            cin>>v>>x;
            a[v-1]=x-ans;
        }
        else if(c==2)
        {
            cin>>x;
            ans+=x;
        }
        else if(c==3)
        {
            cin>>v;
            cout<<a[v-1]+ans<<endl;
        }
    }
    return 0;
}