Problem p03724 (C++)

Buggy submission (status: Time Limit Exceeded):
// Copyright (C) 2017 __debug.

// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; version 3

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program; If not, see <http://www.gnu.org/licenses/>.

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/priority_queue.hpp>

#define x first
#define y second
#define MP std::make_pair
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(), (x).end()
#define DEBUG(...) fprintf(stderr, __VA_ARGS__)
#ifdef __linux__
#define getchar getchar_unlocked
#define putchar putchar_unlocked
#endif

using std::pair;
using std::string;
using std::vector;

typedef long long LL;
typedef pair<int, int> Pii;

const int oo = 0x3f3f3f3f;

template <typename T> inline bool chkmax(T &a, T b) {
  return a < b ? a = b, true : false;
}
template <typename T> inline bool chkmin(T &a, T b) {
  return b < a ? a = b, true : false;
}
string procStatus() {
  std::ifstream t("/proc/self/status");
  return string(std::istreambuf_iterator<char>(t),
                std::istreambuf_iterator<char>());
}
template <typename T> T read(T &x) {
  int f = 1;
  char ch = getchar();
  for (; !isdigit(ch); ch = getchar())
    f = (ch == '-' ? -1 : 1);
  for (x = 0; isdigit(ch); ch = getchar())
    x = 10 * x + ch - '0';
  return x *= f;
}
template <typename T> void write(T x) {
  if (x == 0) {
    putchar('0');
    return;
  }
  if (x < 0) {
    putchar('-');
    x = -x;
  }
  static char s[20];
  int top = 0;
  for (; x; x /= 10)
    s[++top] = x % 10 + '0';
  while (top)
    putchar(s[top--]);
}
// EOT

const int MAXN = 1e5 + 5;

int N, M;
int deg[MAXN];

void input() {
  read(N);
  read(M);
  for (int i = 1; i <= N; ++i) {
    int u, v;
    read(u);
    read(v);
    ++deg[u];
    ++deg[v];
  }
}

void solve() {
  for (int i = 1; i <= N; ++i) {
    if (deg[i] & 1) {
      puts("NO");
      return;
    }
  }
  puts("YES");
}

int main() {
#ifdef __DEBUG
  freopen("B.in", "r", stdin);
  freopen("B.out", "w", stdout);
#endif

  input();
  solve();

  return 0;
}

// 谁料同心结不成，翻就相思结。
//     -- 夏完淳《卜算子·秋色到空闺》


Fixed submission:
// Copyright (C) 2017 __debug.

// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; version 3

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program; If not, see <http://www.gnu.org/licenses/>.

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/priority_queue.hpp>

#define x first
#define y second
#define MP std::make_pair
#define SZ(x) ((int)(x).size())
#define ALL(x) (x).begin(), (x).end()
#define DEBUG(...) fprintf(stderr, __VA_ARGS__)
#ifdef __linux__
#define getchar getchar_unlocked
#define putchar putchar_unlocked
#endif

using std::pair;
using std::string;
using std::vector;

typedef long long LL;
typedef pair<int, int> Pii;

const int oo = 0x3f3f3f3f;

template <typename T> inline bool chkmax(T &a, T b) {
  return a < b ? a = b, true : false;
}
template <typename T> inline bool chkmin(T &a, T b) {
  return b < a ? a = b, true : false;
}
string procStatus() {
  std::ifstream t("/proc/self/status");
  return string(std::istreambuf_iterator<char>(t),
                std::istreambuf_iterator<char>());
}
template <typename T> T read(T &x) {
  int f = 1;
  char ch = getchar();
  for (; !isdigit(ch); ch = getchar())
    f = (ch == '-' ? -1 : 1);
  for (x = 0; isdigit(ch); ch = getchar())
    x = 10 * x + ch - '0';
  return x *= f;
}
template <typename T> void write(T x) {
  if (x == 0) {
    putchar('0');
    return;
  }
  if (x < 0) {
    putchar('-');
    x = -x;
  }
  static char s[20];
  int top = 0;
  for (; x; x /= 10)
    s[++top] = x % 10 + '0';
  while (top)
    putchar(s[top--]);
}
// EOT

const int MAXN = 1e5 + 5;

int N, M;
int deg[MAXN];

void input() {
  read(N);
  read(M);
  for (int i = 1; i <= M; ++i) {
    int u, v;
    read(u);
    read(v);
    ++deg[u];
    ++deg[v];
  }
}

void solve() {
  for (int i = 1; i <= N; ++i) {
    if (deg[i] & 1) {
      puts("NO");
      return;
    }
  }
  puts("YES");
}

int main() {
#ifdef __DEBUG
  freopen("B.in", "r", stdin);
  freopen("B.out", "w", stdout);
#endif

  input();
  solve();

  return 0;
}

// 谁料同心结不成，翻就相思结。
//     -- 夏完淳《卜算子·秋色到空闺》