Problem p02358 (C++) — buggy submission, verdict: Runtime Error

#include <cstdio>
#include <map>
#include <set>
#include <vector>
using namespace std;
long long solve(const vector<pair<pair<int, int>, pair<int, int>>> &v) {
  set<int> lx, ly;
  for (auto &e : v) {
    lx.insert(e.first.first);
    lx.insert(e.second.first);
    ly.insert(e.first.second);
    ly.insert(e.second.second);
  }
  int i;
  map<int, int> mx, my, sx, sy;
  i = 0;
  for (auto ix1 = lx.begin(), ix2 = lx.begin(); ++ix2 != lx.end(); ++ix1, ++i) {
    mx[*ix1] = i, sx[i] = *ix2 - *ix1;
  }
  mx[*lx.rbegin()] = i, sx[i] = 0;
  i = 0;
  for (auto iy1 = ly.begin(), iy2 = ly.begin(); ++iy2 != ly.end(); ++iy1, ++i) {
    my[*iy1] = i, sy[i] = *iy2 - *iy1;
  }
  my[*ly.rbegin()] = i, sy[i] = 0;
  vector<vector<int>> m(my.size());
  for (auto &e : m)
    e.resize(mx.size());
#if 0
	for(auto &e:v){
		for(int x=mx[e.first.first];x<mx[e.second.first];x++)
			for(int y=my[e.first.second];y<my[e.second.second];y++)m[y][x]=1;
	}
#else
  for (auto &e : v) {
    m[my[e.first.second]][mx[e.first.first]]++;
    m[my[e.second.second]][mx[e.first.first]]--;
    m[my[e.first.second]][mx[e.second.first]]--;
    m[my[e.second.second]][mx[e.second.first]]++;
  }
  for (int x = 1; x < sx.size(); x++)
    for (int y = 0; y < sy.size(); y++)
      m[y][x] += m[y][x - 1];
  for (int x = 0; x < sx.size(); x++)
    for (int y = 1; y < sy.size(); y++)
      m[y][x] += m[y - 1][x];
#endif
  long long r = 0;
  for (int x = 0; x < sx.size(); x++)
    for (int y = 0; y < sy.size(); y++)
      if (m[y][x])
        r += (long long)sx[x] * sy[y];
  return r;
}
int main() {
  int N, x1, y1, x2, y2;
  vector<pair<pair<int, int>, pair<int, int>>> v;
  set<int> lx, ly;
  scanf("%d", &N);
  for (int i = 0; i < N; i++) {
    scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
    v.push_back({{x1, y1}, {x2, y2}});
  }
  printf("%lld\\n", solve(v));
}

Error: 0

Fixed submission:

#include <cstdio>
#include <map>
#include <set>
#include <vector>
using namespace std;
long long solve(const vector<pair<pair<int, int>, pair<int, int>>> &v) {
  set<int> lx, ly;
  for (auto &e : v) {
    lx.insert(e.first.first);
    lx.insert(e.second.first);
    ly.insert(e.first.second);
    ly.insert(e.second.second);
  }
  int i;
  map<int, int> mx, my, sx, sy;
  i = 0;
  for (auto ix1 = lx.begin(), ix2 = lx.begin(); ++ix2 != lx.end(); ++ix1, ++i) {
    mx[*ix1] = i, sx[i] = *ix2 - *ix1;
  }
  mx[*lx.rbegin()] = i, sx[i] = 0;
  i = 0;
  for (auto iy1 = ly.begin(), iy2 = ly.begin(); ++iy2 != ly.end(); ++iy1, ++i) {
    my[*iy1] = i, sy[i] = *iy2 - *iy1;
  }
  my[*ly.rbegin()] = i, sy[i] = 0;
  vector<vector<int>> m(my.size());
  for (auto &e : m)
    e.resize(mx.size());
#if 0
	for(auto &e:v){
		for(int x=mx[e.first.first];x<mx[e.second.first];x++)
			for(int y=my[e.first.second];y<my[e.second.second];y++)m[y][x]=1;
	}
#else
  for (auto &e : v) {
    m[my[e.first.second]][mx[e.first.first]]++;
    m[my[e.second.second]][mx[e.first.first]]--;
    m[my[e.first.second]][mx[e.second.first]]--;
    m[my[e.second.second]][mx[e.second.first]]++;
  }
  for (int x = 1; x < sx.size(); x++)
    for (int y = 0; y < sy.size(); y++)
      m[x][y] += m[x - 1][y];
  for (int x = 0; x < sx.size(); x++)
    for (int y = 1; y < sy.size(); y++)
      m[x][y] += m[x][y - 1];
#endif
  long long r = 0;
  for (int x = 0; x < sx.size(); x++)
    for (int y = 0; y < sy.size(); y++)
      if (m[y][x])
        r += sx[x] * sy[y];
  return r;
}
int main() {
  int N, x1, y1, x2, y2;
  vector<pair<pair<int, int>, pair<int, int>>> v;
  set<int> lx, ly;
  scanf("%d", &N);
  for (int i = 0; i < N; i++) {
    scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
    v.push_back({{x1, y1}, {x2, y2}});
  }
  printf("%lld\\n", solve(v));
}