In this HackerRank The Value of Friendship problem solution You are given q queries, where each query is in the form of an unordered list of m distinct direct friendships between n students. For each query, find the maximum value of total among all possible orderings of formed friendships and print it on a new line.
Problem solution in Python.
def grow(n):
res = 0
for i in range(1, n):
res += i*(i+1)
#print("-->", i, res)
return res
def mark(x):
z = x
while z: z = z[0]
if x is not z: x[0] = z
return z
def mark2(x):
z = x
while z and type(z) == list: z = z[0]
if x is not z: x[0] = z
return z
T = int(input())
for t in range(T):
n, m = map(int, input().split())
work = [[] for i in range(n)]
lost = 0
for i in range(m):
u, v = map(int, input().split())
u -= 1
v -= 1
mu = mark(work[u])
mv = mark(work[v])
if mu is not mv:
mu.append(mv)
else:
lost += 1
no = 1
dic = {}
for i in range(n):
z = mark2(work[i])
if not z:
z.append(no)
z = no
no += 1
dic[z] = 1
else:
dic[z] += 1
res = 0
cur = 0
for v in sorted(dic.values(), reverse = True):
res += grow(v) + (v-1) * cur
cur += v*(v-1)
#print(v, cur, res)
res += lost * cur
print(res)
Problem solution in Java.
import java.util.*;
public class Solution {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int t = in.nextInt();
for(int a0 = 0; a0 < t; a0++){
int n = in.nextInt();
int m = in.nextInt();
DisjointSets friendGroups = new DisjointSets(n);
for(int a1 = 0; a1 < m; a1++){
int x = in.nextInt();
int y = in.nextInt();
// your code goes here
friendGroups.union(x - 1, y - 1);
}
List<Integer> groupSizes = friendGroups.setSizes();
Collections.sort(groupSizes, Comparator.reverseOrder());
long[] extra = new long[m];
int idx = 0;
for (int size : groupSizes) {
for (int i = 1; i < size; i++) {
extra[idx++] = i;
}
}
long totalFriendship = 0;
long currentFriendship = 0;
for (int i = 0; i < m; i++) {
currentFriendship += 2L * extra[i];
totalFriendship += currentFriendship;
}
System.out.println(totalFriendship);
}
}
private static class DisjointSets {
private int[] parent;
private int[] size;
public DisjointSets(int n) {
parent = new int[n];
size = new int[n];
for (int i = 0; i < n; i++) {
parent[i] = i;
size[i] = 1;
}
}
public void union(int a, int b) {
int p = find(a);
int q = find(b);
if (p == q)
return;
if (size[p] < size[q]) {
parent[p] = q;
size[q] += size[p];
}
else {
parent[q] = p;
size[p] += size[q];
}
}
public int find(int x) {
while (x != parent[x]) {
parent[x] = parent[parent[x]];
x = parent[x];
}
return x;
}
public List<Integer> setSizes() {
Set<Integer> sets = new HashSet<>();
for (int x : parent)
sets.add(find(x));
List<Integer> sizes = new ArrayList<>();
for (int x : sets)
sizes.add(size[x]);
return sizes;
}
}
}
Problem solution in C++.
#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>
using namespace std;
vector<int> parent, setSz;
int find(int x)
{
if (parent[x] == x)
return x;
return parent[x] = find(parent[x]);
}
int setunion(int a, int b)
{
a = find(a);
b = find(b);
if (a == b)
return setSz[a];
if (setSz[a] < setSz[b])
swap(a, b);
parent[b] = a;
setSz[a] += setSz[b];
return setSz[a];
}
#define lint long long int
int main() {
int t;
cin >> t;
for (int a0 = 0; a0 < t; a0++) {
int n;
int m;
cin >> n >> m;
parent.clear();
parent.resize(n + 1);
for (int i = 1; i <= n; i++)
parent[i] = i;
setSz.clear();
setSz.resize(n + 1, 1);
lint curFr = 0;
lint res = 0;
int same = 0;
for (int a1 = 0; a1 < m; a1++) {
int x;
int y;
cin >> x >> y;
if (find(x) == find(y))
same++;
setunion(x, y);
//lint oldSz1 = setSz[find(x)];
//lint oldSz2 = setSz[find(y)];
//lint newSz = setunion(x, y);
//curFr += (newSz * (newSz - 1LL)) - (oldSz1 * (oldSz1 - 1LL)) - (oldSz2 * (oldSz2 - 1LL));
//res += curFr;
//cout << newSz << " " << curFr << endl;
}
set<int> clusters;
vector<int> clusterSz;
for (int i = 1; i <= n; i++)
{
int x = find(i);
if (clusters.find(x) != clusters.end())
continue;
clusterSz.push_back(setSz[x]);
clusters.insert(x);
}
sort(clusterSz.begin(), clusterSz.end());
for (int i = clusterSz.size() - 1; i >= 0; i--)
{
for (int j = 2; j <= clusterSz[i]; j++)
{
curFr += j * (j - 1) - (j - 1) * (j - 2);
res += curFr;
}
}
res += curFr * same;
cout << res << endl;
}
return 0;
}
Problem solution in C.
#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
#include <string.h>
#include <stdlib.h>
int n, m;
int graph[500002][2]; // [0]-neighbor node, [1]-next
int gend;
int nodeedge[100001];
int used[100001];
int bfs(int v, int *edgen) {
int q[100001];
int i, j, qe=1;
q[0]=v;
used[v]=1;
*edgen=nodeedge[v];
for (i=0; i<qe; i++) {
for (j=q[i]; j && (v=graph[j][0]); j=graph[j][1]) {
if (!used[v]) {
q[qe++]=v;
used[v]=1;
*edgen+=nodeedge[v];
}
}
}
return qe;
}
static int cmp(const void *p1, const void *p2) {
return *((const int *)p2)-*((const int *)p1);
}
uint64_t solve(void) {
uint64_t total=0, tt=0, t;
int noden[100001], edgen, rededgen=0;
int i, nni=0;
for (i=1; i<=n; i++) {
if (used[i])
continue;
noden[nni]=bfs(i, &edgen);
if (edgen)
rededgen+=edgen-noden[nni++]+1;
}
qsort(noden, nni, sizeof(int), cmp);
for (i=0; i<nni; i++) {
t=noden[i];
total+=(t*(t+1)*(t-1))/3+(t-1)*tt;
tt+=t*(t-1);
}
total+=tt*rededgen;
return total;
}
int main(void) {
int i, q, u, v;
scanf("%d\n", &q);
while (q--) {
scanf("%d%d\n", &n, &m);
gend=n+1;
for (i=0; i<m; i++) {
scanf("%d%d\n", &u, &v);
if (graph[u][0]) {
graph[gend][0]=graph[u][0];
graph[gend][1]=graph[u][1];
graph[u][0]=v;
graph[u][1]=gend++;
} else {
graph[u][0]=v;
}
if (graph[v][0]) {
graph[gend][0]=graph[v][0];
graph[gend][1]=graph[v][1];
graph[v][0]=u;
graph[v][1]=gend++;
} else {
graph[v][0]=u;
}
nodeedge[u]++;
}
printf("%"PRIu64"\n", solve());
memset(graph, 0, sizeof(graph));
memset(nodeedge, 0, sizeof(nodeedge));
memset(used, 0, sizeof(used));
gend=0;
}
return 0;
}
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