Language: C++

//============================================================================
//Everyone has a different way of thinking, so God Created us
//   Hope You Respect My Way..,Thank You ):
// Author      : Murad
// Name        : Codeforces.cpp & Atcoder.cpp
// Description : Problem name
//============================================================================
#include<bits/stdc++.h>
#include<unordered_map>
#include<unordered_set>
using namespace std;
#define pi 3.1415926536
#define forn(i,a,b)for(int i=a;i<b;i++)
#define LL long long
#define ULL unsigned long long
#define MP make_pair
#define ff first
#define ss second
#define endl '\n'
#define INF 1e9 + 1
#define _INF INT32_MIN
#define PQ priority_queue
#define MM multimap
#define PB push_back
#define vii vector<int>
#define ipair pair<int,int>
#define lpair pair<LL,LL>
#define MAXN 100004
#define El3zba ios::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define modd 1000000007
#define sfll1(v) scanf("%I64d",&v);
#define sfll2(v1,v2) scanf("%I64d %I64d",&v1,&v2)
#define sfll3(v1,v2,v3) scanf("%I64d %I64d %I64d",&v1,&v2,&v3)
//std::transform(s1.begin(), s1.end(), s1.begin(),::tolower);
char alphz[27] = { 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z' };
float Euclidean(LL x1, LL x2, LL y1, LL y2) {
	return sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2));
}
LL gcd(LL a,LL b) {
	LL c;
	while (a != 0) {
		c = a;
		a = b % a;
		b = c;
	}
	return b;
}
LL LCM(LL a, LL b) {
	return (a*b) / gcd(a, b);
}
void PrimeFactor(LL n)
{
	while (n % 2 == 0) {
		printf("%d ", 2);
		n /= 2;
	}
	for (int i = 3; i <= sqrt(n); i += 2)
	{
		if (n%i == 0) {
			printf("%d ", i);
			n /= i;
		}
	}
	if (n > 2)printf("%d ", n);
}
bool is_square(LL x) {
	LL l = 0, r = x;
	while (l <= r) {
		LL mid = l + (r - l) / 2;
		if (mid*mid == x)return true;
		if (mid*mid > x)r = mid - 1;
		else l = mid + 1;
	}
	return false;
}
LL power(LL x, LL y)
{
	LL temp;
	if (y == 0)return 1;
	temp = power(x, y / 2);
	if (y % 2 == 0)
		return temp*temp;
	else return x*temp*temp;
}
bool is_Prime(int x) {
	if (x == 2)return 1;
	else if (x % 2 == 0 || x < 2)return 0;
	for (int i = 3; i*i <= x; i += 2)
		if (x%i == 0)return 0;
	return 1;
}
deque<int>sol[100005];
map<ipair, int>mpp;
map<int, int>idxz;
int main()
{
	El3zba;
	/***  بسم الله الرحمن الرحيم   ***/
	int n, m;
	cin >> n >> m;
	vector<ipair>a;
	for (int i = 0; i < m; i++)
	{
		int x, y;
		cin >> x >> y;
		a.PB({ x,y });
		sol[x].PB(y);
		if (idxz[x] > 0)
		{
			mpp[{y, x}] = idxz[x] + 1;
			idxz[x]++;
		}
		else mpp[{y, x}]++, idxz[x]++;
	}
	int idx = 1;
	auto &v = mpp.begin();
	int prev = v->ff.ss;
	for (auto&x : mpp)
	{
		if (x.ff.ss == prev)
		{
			mpp[{x.ff.ff,x.ff.ss}] = idx;
			idx++;
		}
		else
		{
			prev = x.ff.ss;
			mpp[{x.ff.ff, x.ff.ss}] = 1;
			idx = 2;
		}
	}
	for (auto&x : a)
	{
		string ans = "";
		swap(x.ff, x.ss);
		int v = mpp[{x.ff, x.ss}];
		string wal = to_string(x.ss);
		ans += wal;
		wal = to_string(v);
		while ((int)ans.size() < 6)
		{
			ans.insert(0, "0");
		}
		for (int i = (int)ans.size(); i <= 11 - (int)wal.size(); i++)
			ans.insert(i, "0");
		ans += wal;
		cout << ans << endl;
	}
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:116:28: error: cannot bind non-const lvalue reference of type 'std::_Rb_tree_iterator<std::pair<const std::pair<int, int>, int> >&' to an rvalue of type 'std::map<std::pair<int, int>, int>::iterator' {aka 'std::_Rb_tree<std::pair<int, int>, std::pair<const std::pair<int, int>, int>, std::_Select1st<std::pair<const std::pair<int, int>, int> >, std::less<std::pair<int, int> >, std::allocator<std::pair<const std::pair<int, int>, int> > >::iterator'}
  116 |         auto &v = mpp.begin();
      |                   ~~~~~~~~~^~