Far Vertices
Problem Statement :
You are given a tree that has N vertices and N-1 edges. Your task is to mark as small number of vertices as possible, such that, the maximum distance between two unmarked vertices is less than or equal to K. Output this value. Distance between two vertices i and j is defined as the minimum number of edges you have to pass in order to reach vertex i from vertex j. Input Format The first line of input contains two integers N and K. The next N-1 lines contain two integers (ui,vi) each, where 1 <= ui,vi <= N. Each of these lines specifies an edge. N is no more than 100. K is less than N. Output Format Print an integer that denotes the result of the test.
Solution :
Solution in C :
In C++ :
#include <queue>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <string.h>
#include <limits.h>
using namespace std;
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define ll long long int
#define ii pair<int,int>
#define Clear(x,val) memset(x,val,sizeof(x))
#define SZ(v) (v).size()
#define maxv 200
vector < vector<int> > vv(200);
int a[maxv][maxv];
int visited[maxv];
int val[maxv];
int main()
{
for( int i = 0; i < maxv; i++ ) for( int j = 0; j < maxv; j++ ) a[i][j] = 1e9;
int n , K; cin >> n >> K;
for( int i = 1;i < n; i++ ) {
int x , y;
cin >> x >> y;
--x;--y;
a[x][y] = min( a[x][y] , 1 );
a[y][x] = min( a[y][x] , 1 );
vv[x].push_back(y);
vv[y].push_back(x);
}
for( int i = 0; i < n; i++ ) a[i][i] = 0;
int ans = 0;
for( int k = 0; k < n; k++ )
for( int i = 0; i < n; i++ )
for( int j = 0; j < n; j++ )
a[i][j] = min( a[i][j] , a[i][k]+a[k][j] );
Clear( visited , 0 );Clear( val , 0 );
int u = -1;
for( int i = 0; i < n; i++ ) {
u = -1;
for( int j = n-1; j >= 0; j-- ) {
if( !visited[j] && ( u<0 || val[j]>val[u] ) )
u = j;
}
visited[u] = 1;int tmp = 0;
for( int i = 0; i < n; i++ ) if( a[u][i] <= K ) {
if( visited[i] ) ++tmp;
else val[i] += 1;
}
ans = max( ans , tmp );
}
cout << n-ans << "\n";
return 0;
}
In Java :
import java.util.LinkedList;
import java.util.Scanner;
public class Solution {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int k = scanner.nextInt();
LinkedList[] adjacencyList = new LinkedList[n];
for (int i = 0; i < n; i++) {
adjacencyList[i] = new LinkedList<Integer>();
}
for (int i = 0; i < n - 1; i++) {
int node1 = scanner.nextInt();
int node2 = scanner.nextInt();
node1--;
node2--;
adjacencyList[node1].add(node2);
adjacencyList[node2].add(node1);
}
int[][] farMatrix = new int[n][n];
for (int i = 0; i < n; i++) {
LinkedList<Integer> queue = new LinkedList<Integer>();
LinkedList<Integer> queuedistance = new LinkedList<Integer>();
boolean explored[] = new boolean[n];
for (int j = 0; j < n; j++) {
explored[j] = false;
}
queue.add(i);
queuedistance.add(0);
explored[i] = true;
while (queue.isEmpty() == false) {
int node = queue.removeFirst();
int distance = queuedistance.removeFirst();
farMatrix[i][node] = distance;
for (Object adj : adjacencyList[node]) {
Integer adjNode = (Integer) adj;
if (explored[adjNode] == false) {
queue.add(adjNode);
queuedistance.add(distance + 1);
explored[adjNode] = true;
}
}
}
}
int count = 0;
while (true) {
int longestDistance = -1;
int longestI = -1, longestJ = -1;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (farMatrix[i][j] > longestDistance) {
longestDistance = farMatrix[i][j];
longestI = i;
longestJ = j;
}
}
}
if (longestDistance <= k) {
break;
}
count++;
int iCount = 0;
for (int i = 0; i < n; i++) {
if (farMatrix[longestI][i] > k) {
iCount++;
}
}
int jCount = 0;
for (int i = 0; i < n; i++) {
if (farMatrix[longestJ][i] > k) {
jCount++;
}
}
// remove longestI
if (iCount > jCount) {
for (int i = 0; i < n; i++) {
farMatrix[longestI][i] = 0;
farMatrix[i][longestI] = 0;
}
} else {
for (int i = 0; i < n; i++) {
farMatrix[longestJ][i] = 0;
farMatrix[i][longestJ] = 0;
}
}
}
System.out.println(count);
}
}
In C :
#include <stdio.h>
long long b[1000],a[1000][1000],i,j,k,l,m,n,t,K;
long long makaj(long long ii, long long jj, long long hh)
{
long long vv=0,tt;
for(tt=0;tt<n;tt++)
{
if(a[tt][jj]<a[tt][ii] && a[tt][ii]<=hh) vv++;
if(a[tt][jj]>a[tt][ii] && a[tt][ii]<=K-hh) vv++;
}
return vv;
}
int main()
{
scanf("%lld %lld\n",&n,&K);
for(i=0;i<n;i++)
for(j=0;j<n;j++) a[i][j] = 100000000;
for(i=0;i<n;i++) a[i][i]=0;
for(i=0;i<n-1;i++)
{
scanf("%lld %lld",&j,&l);
a[j-1][l-1]=1;
a[l-1][j-1]=1;
}
for(k=0;k<n;k++)
for(i=0;i<n;i++)
for(j=0;j<n;j++)
if(a[i][j]> a[i][k] + a[k][j])
{
a[i][j] = a[j][i] = a[i][k]+a[k][j];
}
m = 100000;
for(i=0;i<n;i++)
for(j=0;j<n;j++)
if(a[i][j]==1)
{
for(l=K;l>=(K+1)/2;l--)
k = makaj(i,j,l);
if(n-k<m) m = n-k;
}
printf("%lld\n",m);
//for(i=0;i<n;i++)
// for(j=0;j<n;j++)
// printf("%lld %lld -> %lld\n",i,j,a[i][j]);
return 0;
}
In Python3 :
#!/bin/python3
import os
import sys
from collections import Counter
def farVertices(n, k, edges):
tree = {}
for edge in edges:
tree[edge[0],edge[1]] = 1
tree[edge[1],edge[0]] = 1
tree_paths = len(tree)
cont_flag = True
while cont_flag:
for edge in edges:
matches = {x:y for x,y in tree.items() if edge[1] == x[0]}
for match in matches.keys():
if (edge[0],match[1]) not in tree.keys() and edge[0] != match[1]:
tree[edge[0],match[1]] = matches[match] + 1
tree[match[1],edge[0]] = matches[match] + 1
matches = {x:y for x,y in tree.items() if edge[0] == x[1]}
for match in matches.keys():
if (edge[1],match[0]) not in tree.keys() and edge[1] != match[0]:
tree[edge[1],match[0]] = matches[match] + 1
tree[match[0],edge[1]] = matches[match] + 1
if len(tree) == tree_paths:
cont_flag = False
tree_paths = len(tree)
removed = 0
cont_flag = True
while cont_flag:
matches = [x[0] for x,y in tree.items() if y>k]
if len(matches)==0:
cont_flag = False
else:
removed += 1
match_count = Counter(matches)
maxcount = max([y for x,y in match_count.items()])
match_max = [x for x,y in match_count.items() if y==maxcount]
remove_node = match_max[0]
nodes_to_remove = [x for x in tree.keys() if
x[0]==remove_node or x[1]==remove_node]
print(nodes_to_remove)
for node in nodes_to_remove:
del tree[node]
return removed
if __name__ == '__main__':
fptr = open(os.environ['OUTPUT_PATH'], 'w')
nk = input().split()
n = int(nk[0])
k = int(nk[1])
edges = []
for _ in range(n-1):
edges.append(list(map(int, input().rstrip().split())))
result = farVertices(n, k, edges)
fptr.write(str(result) + '\n')
fptr.close()
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