Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của flashmt

#include <bits/stdc++.h>
using namespace std;

int n, cntDist[3333];
vector <int> a[3333];

void bfs(int x)
{
    queue <int> q;
    int dist[3333];

    for (int i = 1; i <= n; i++) dist[i] = -1;
    dist[x] = 0;
    q.push(x);

    while (!q.empty())
    {
        int x = q.front();
        q.pop();
        cntDist[dist[x]]++;

        for (int i = 0; i < int(a[x].size()); i++)
        {
            int y = a[x][i];
            if (dist[y] < 0) dist[y] = dist[x] + 1, q.push(y);
        }
    }
}

int main()
{
    int m, x, y;

    cin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        cin >> x >> y;
        a[x].push_back(y);
        a[y].push_back(x);
    }

    for (int i = 1; i <= n; i++) bfs(i);

    for (int i = 1; ; i++)
    {
        int cnt = 0;
        for (int d = (1 << (i - 1)) + 1; d <= 1 << i; d++) cnt += cntDist[d];
        cout << cnt / 2 << ' ';
        if (!cnt) break;
    }
}

Code mẫu của ladpro98

#include <bits/stdc++.h>
const int N = 3003;
const double eps = 1e-6;
using namespace std;
int Q[N], d[N][N], res[N];
vector<int> a[N];
int n, m;

void BFS(int s) {
    int l = 1, r = 1, i, u, v;
    Q[1] = s; d[s][s] = 1;
    while (l <= r) {
        u = Q[l++];
        for(i = 0; i < a[u].size(); i++) {
            v = a[u][i];
            if (d[s][v] == 0) {
                d[s][v] = d[s][u] + 1;
                Q[++r] = v;
            }
        }
    }
}

int main()
{
    scanf("%d %d", &n, &m);
    int i, j, u, v;
    for(i = 1; i <= m; i++) {
        scanf("%d %d", &u, &v);
        a[u].push_back(v); a[v].push_back(u);
    }
    for(i = 1; i <= n; i++) BFS(i);
    for(i = 1; i < n; i++) for(j = i + 1; j <= n; j++) {
        int day = round(log2(d[i][j] - 1));
        if ((1 << day) < d[i][j] - 1) day++;
        res[day]++;
    }
    for(i = 1; i <= n; i++) {
        printf("%d ", res[i]);
        if (res[i] == 0) break;
    }
    return 0;
}

Code mẫu của hieult

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <fstream>
#include <ctime>
#include <deque>
#include <bitset>
#include <cctype>
#include <utility>
#include <cassert>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned int ui;
typedef unsigned long long ull;

#define Rep(i,n) for(int i = 0; i < (n); ++i)
#define Repd(i,n) for(int i = (n)-1; i >= 0; --i)
#define For(i,a,b) for(int i = (a); i <= (b); ++i)
#define Ford(i,a,b) for(int i = (a); i >= (b); --i)
#define Fit(i,v) For(__typeof((v).begin()) i = (v).begin(); i != (v).end(); ++i)
#define Fitd(i,v) For(__typeof((v).rbegin()) i = (v).rbegin(); i != (v).rend(); ++i)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define sz(a) ((int)(a).size())
#define all(a) (a).begin(), (a).end()
#define ms(a,x) memset(a, x, sizeof(a))

template<class F, class T> T convert(F a, int p = -1) { stringstream ss; if (p >= 0) ss << fixed << setprecision(p); ss << a; T r; ss >> r; return r; }
template<class T> T gcd(T a, T b) { T r; while (b != 0) { r = a % b; a = b; b = r; } return a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template<class T> T sqr(T x) { return x * x; }
template<class T> T cube(T x) { return x * x * x; }
template<class T> int getbit(T s, int i) { return (s >> i) & 1; }
template<class T> T onbit(T s, int i) { return s | (T(1) << i); }
template<class T> T offbit(T s, int i) { return s & (~(T(1) << i)); }
template<class T> int cntbit(T s) { return __builtin_popcount(s); }
const int bfsz = 1 << 16; char bf[bfsz + 5]; int rsz = 0;int ptr = 0;
char gc() { if (rsz <= 0) { ptr = 0; rsz = (int) fread(bf, 1, bfsz, stdin); if (rsz <= 0) return EOF; } --rsz; return bf[ptr++]; }
void ga(char &c) { c = EOF; while (!isalpha(c)) c = gc(); }
int gs(char s[]) { int l = 0; char c = gc(); while (isspace(c)) c = gc(); while (c != EOF && !isspace(c)) { s[l++] = c; c = gc(); } s[l] = '\0'; return l; }
template<class T> bool gi(T &v) {
    v = 0; char c = gc(); while (c != EOF && c != '-' && !isdigit(c)) c = gc(); if (c == EOF) return false; bool neg = c == '-'; if (neg) c = gc();
    while (isdigit(c)) { v = v * 10 + c - '0'; c = gc(); } if (neg) v = -v; return true;
}

typedef pair<int, int> II;

const ld PI = acos(ld(-1.0));
const ld eps = 1e-9;

const int inf = (int)1e9 + 5;
const ll linf = (ll)1e17 + 5;
int dr[8] = {-1, +1, 0, 0, +1, +1, -1, -1};
int dc[8] = {0, 0, +1, -1, -1, +1, -1, +1};
const ll mod = 1000000007;

#define maxn 100005

int n, m;
int adj[maxn], next[maxn], last[maxn], f[maxn], E = 0;
int que[maxn], size, d[maxn];

void add(int u, int v){
    adj[E] = v; next[E] = last[u]; last[u] = E++;
    adj[E] = u; next[E] = last[v]; last[v] = E++;
}

void go(int u){
    size = 0;
    que[size++] = u;
    For(i, 1, n) d[i] = -1;
    d[u] = 0;
    Rep(i, size){
        u = que[i];
        f[d[u]]++;
        for(int e = last[u]; e != -1; e = next[e]){
            int v = adj[e];
            if(d[v] == -1){
                d[v] = d[u] + 1;
                que[size++] = v;
            }
        }
    }
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
//    freopen("in.txt", "r", stdin);
    cin >> n >> m;
    int u, v;
    ms(last, -1); E = 0;
    ms(f, 0);
    Rep(run, m){
        cin >> u >> v;
        add(u, v);
    }

    For(i, 1, n) go(i);
    for(int i = 1;; i++){
        int res = 0;
        For(j, (1 << (i - 1)) + 1, 1 << i){
            res += f[j];
        }
        cout << res / 2 << " ";
        if(res == 0) break;
    }

    return 0;

}

Code mẫu của skyvn97

#include<algorithm>
#include<cstdio>
#include<cstring>
#include<queue>
#include<vector>
#define MAX   3030
#define FOR(i,a,b) for (int i=(a);i<=(b);i=i+1)
#define REP(i,n) for (int i=0;i<(n);i=i+1)
using namespace std;
vector<int> g[MAX];
int d[MAX][MAX];
int f[MAX];
int c[MAX];
int m,n,q;
void loadgraph(void) {
    scanf("%d",&n);
    scanf("%d",&m);
    REP(i,m) {
        int u,v;
        scanf("%d",&u);
        scanf("%d",&v);
        g[u].push_back(v);
        g[v].push_back(u);
    }
    memset(d,-1,sizeof d);
    q=1;
    f[1]=2;
    while (f[q]<=n) {
        q++;
        f[q]=2*f[q-1];
    }
}
void BFS(int s) {
    queue<int> q;
    while (!q.empty()) q.pop();
    d[s][s]=0;
    q.push(s);
    while (!q.empty()) {
        int u=q.front();q.pop();
        REP(i,g[u].size()) if (d[s][g[u][i]]<0) {
            d[s][g[u][i]]=d[s][u]+1;
            q.push(g[u][i]);
        }
    }
}
int minstep(int x) {        
    return (lower_bound(f+1,f+1+q,x)-f);
}
void process(void) {    
    FOR(i,1,n) BFS(i);  
    FOR(i,1,n) FOR(j,i+1,n) if (d[i][j]>1) c[minstep(d[i][j])]++;
    int j=0;
    while (true) {
        j++;
        printf("%d",c[j]);
        if (c[j]==0) break;
        else printf(" ");
    }
}
int main(void) {
    loadgraph();
    process();
    return 0;
}