In this HackerRank Jumping Rooks problem solution, You have Given the configuration of the chessboard and some k, help Nina place k jumping rooks in the chessboard’s free cells such that the number of pairs of rooks that beat each other is minimal. Then print a single integer denoting the number of rooks that beat each other.
Problem solution in Java.
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.List;
public class C {
InputStream is;
PrintWriter out;
String INPUT = "";
void solve()
{
int n = ni(), K = ni();
char[][] map = nm(n,n);
int[][] ud = new int[n][n];
int[][] lr = new int[n][n];
int pud = 0, plr = 0;
{
int id = -1;
for(int i = 0;i < n;i++){
char pre = 0;
for(int j = 0;j < n;j++){
if(map[j][i] == '.'){
if(pre != '.')id++;
ud[j][i] = id;
}
pre = map[j][i];
}
}
pud = id + 1;
}
{
int id = -1;
for(int i = 0;i < n;i++){
char pre = 0;
for(int j = 0;j < n;j++){
if(map[i][j] == '.'){
if(pre != '.')id++;
lr[i][j] = id;
}
pre = map[i][j];
}
}
plr = id + 1;
}
List<Edge> es = new ArrayList<>();
for(int i = 0;i < n;i++){
for(int j = 0;j < n;j++){
if(map[i][j] == '.'){
es.add(new Edge(ud[i][j], lr[i][j]+pud, 1, 0));
}
}
}
int src = pud + plr, sink = src + 1;
for(int i = 0;i < pud;i++){
for(int j = 0;j <= n;j++){
es.add(new Edge(src, i, 1, j));
}
}
for(int i = 0;i < plr;i++){
for(int j = 0;j <= n;j++){
es.add(new Edge(i+pud, sink, 1, j));
}
}
out.println(solveMinCostFlow(compileWD(sink+1, es), src, sink, K));
}
public static class Edge
{
public int from, to;
public int capacity;
public int cost;
public int flow;
public Edge complement;
// public int iniflow;
public Edge(int from, int to, int capacity, int cost) {
this.from = from;
this.to = to;
this.capacity = capacity;
this.cost = cost;
}
}
public static Edge[][] compileWD(int n, List<Edge> edges)
{
Edge[][] g = new Edge[n][];
// cloning
for(int i = edges.size()-1;i >= 0;i--){
Edge origin = edges.get(i);
Edge clone = new Edge(origin.to, origin.from, origin.capacity, -origin.cost);
clone.flow = origin.capacity;
clone.complement = origin;
origin.complement = clone;
edges.add(clone);
}
int[] p = new int[n];
for(Edge e : edges)p[e.from]++;
for(int i = 0;i < n;i++)g[i] = new Edge[p[i]];
for(Edge e : edges)g[e.from][--p[e.from]] = e;
return g;
}
// NOT VERIFIED
public static Edge[][] compileWU(int n, List<Edge> edges)
{
Edge[][] g = new Edge[n][];
// cloning
for(int i = edges.size()-1;i >= 0;i--){
Edge origin = edges.get(i);
Edge back = new Edge(origin.to, origin.from, origin.capacity, origin.cost);
edges.add(back);
}
for(int i = edges.size()-1;i >= 0;i--){
Edge origin = edges.get(i);
Edge clone = new Edge(origin.to, origin.from, origin.capacity, -origin.cost);
clone.flow = origin.capacity;
clone.complement = origin;
origin.complement = clone;
edges.add(clone);
}
int[] p = new int[n];
for(Edge e : edges)p[e.from]++;
for(int i = 0;i < n;i++)g[i] = new Edge[p[i]];
for(Edge e : edges)g[e.from][--p[e.from]] = e;
return g;
}
public static long solveMinCostFlow(Edge[][] g, int source, int sink, long all)
{
int n = g.length;
long mincost = 0;
int[] potential = new int[n];
final int[] d = new int[n];
MinHeap q = new MinHeap(n);
while(all > 0){
// shortest path src->sink
Edge[] inedge = new Edge[n];
Arrays.fill(d, Integer.MAX_VALUE / 2);
d[source] = 0;
q.add(source, 0);
while(q.size() > 0){
int cur = q.argmin();
q.remove(cur);
for(Edge ne : g[cur]){
if(ne.capacity - ne.flow > 0){
int nd = d[cur] + ne.cost + potential[cur] - potential[ne.to];
if(d[ne.to] > nd){
inedge[ne.to] = ne;
d[ne.to] = nd;
q.update(ne.to, nd);
}
}
}
}
if(inedge[sink] == null)break;
long minflow = all;
long sumcost = 0;
for(Edge e = inedge[sink];e != null;e = inedge[e.from]){
if(e.capacity - e.flow < minflow)minflow = e.capacity - e.flow;
sumcost += e.cost;
}
mincost += minflow * sumcost;
for(Edge e = inedge[sink];e != null;e = inedge[e.from]){
e.flow += minflow;
e.complement.flow -= minflow;
}
all -= minflow;
for(int i = 0;i < n;i++){
potential[i] += d[i];
}
}
return mincost;
}
public static class MinHeap {
public int[] a;
public int[] map;
public int[] imap;
public int n;
public int pos;
public static int INF = Integer.MAX_VALUE;
public MinHeap(int m)
{
n = m+2;
a = new int[n];
map = new int[n];
imap = new int[n];
Arrays.fill(a, INF);
Arrays.fill(map, -1);
Arrays.fill(imap, -1);
pos = 1;
}
public int add(int ind, int x)
{
int ret = imap[ind];
if(imap[ind] < 0){
a[pos] = x; map[pos] = ind; imap[ind] = pos;
pos++;
up(pos-1);
}
return ret != -1 ? a[ret] : x;
}
public int update(int ind, int x)
{
int ret = imap[ind];
if(imap[ind] < 0){
a[pos] = x; map[pos] = ind; imap[ind] = pos;
pos++;
up(pos-1);
}else{
int o = a[ret];
a[ret] = x;
up(ret);
down(ret);
// if(a[ret] > o){
// up(ret);
// }else{
// down(ret);
// }
}
return x;
}
public int remove(int ind)
{
if(pos == 1)return INF;
if(imap[ind] == -1)return INF;
pos--;
int rem = imap[ind];
int ret = a[rem];
map[rem] = map[pos];
imap[map[pos]] = rem;
imap[ind] = -1;
a[rem] = a[pos];
a[pos] = INF;
map[pos] = -1;
up(rem);
down(rem);
return ret;
}
public int min() { return a[1]; }
public int argmin() { return map[1]; }
public int size() { return pos-1; }
private void up(int cur)
{
for(int c = cur, p = c>>>1;p >= 1 && a[p] > a[c];c>>>=1, p>>>=1){
int d = a[p]; a[p] = a[c]; a[c] = d;
int e = imap[map[p]]; imap[map[p]] = imap[map[c]]; imap[map[c]] = e;
e = map[p]; map[p] = map[c]; map[c] = e;
}
}
private void down(int cur)
{
for(int c = cur;2*c < pos;){
int b = a[2*c] < a[2*c+1] ? 2*c : 2*c+1;
if(a[b] < a[c]){
int d = a[c]; a[c] = a[b]; a[b] = d;
int e = imap[map[c]]; imap[map[c]] = imap[map[b]]; imap[map[b]] = e;
e = map[c]; map[c] = map[b]; map[b] = e;
c = b;
}else{
break;
}
}
}
}
void run() throws Exception
{
is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
out = new PrintWriter(System.out);
long s = System.currentTimeMillis();
solve();
out.flush();
if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
}
public static void main(String[] args) throws Exception { new C().run(); }
private byte[] inbuf = new byte[1024];
private int lenbuf = 0, ptrbuf = 0;
private int readByte()
{
if(lenbuf == -1)throw new InputMismatchException();
if(ptrbuf >= lenbuf){
ptrbuf = 0;
try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
if(lenbuf <= 0)return -1;
}
return inbuf[ptrbuf++];
}
private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
private double nd() { return Double.parseDouble(ns()); }
private char nc() { return (char)skip(); }
private String ns()
{
int b = skip();
StringBuilder sb = new StringBuilder();
while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
sb.appendCodePoint(b);
b = readByte();
}
return sb.toString();
}
private char[] ns(int n)
{
char[] buf = new char[n];
int b = skip(), p = 0;
while(p < n && !(isSpaceChar(b))){
buf[p++] = (char)b;
b = readByte();
}
return n == p ? buf : Arrays.copyOf(buf, p);
}
private char[][] nm(int n, int m)
{
char[][] map = new char[n][];
for(int i = 0;i < n;i++)map[i] = ns(m);
return map;
}
private int[] na(int n)
{
int[] a = new int[n];
for(int i = 0;i < n;i++)a[i] = ni();
return a;
}
private int ni()
{
int num = 0, b;
boolean minus = false;
while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
if(b == '-'){
minus = true;
b = readByte();
}
while(true){
if(b >= '0' && b <= '9'){
num = num * 10 + (b - '0');
}else{
return minus ? -num : num;
}
b = readByte();
}
}
private long nl()
{
long num = 0;
int b;
boolean minus = false;
while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
if(b == '-'){
minus = true;
b = readByte();
}
while(true){
if(b >= '0' && b <= '9'){
num = num * 10 + (b - '0');
}else{
return minus ? -num : num;
}
b = readByte();
}
}
private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); }
}
Problem solution in C++.
#include <cstdio>
#include <vector>
#include <queue>
#include <cstring>
using namespace std;
#define INF 1000000000
#define maxn 10002
struct Edge
{
int from, to, cap, flow, cost;
Edge(int u, int v, int c, int f, int w) : from(u), to(v), cap(c), flow(f), cost(w) {}
};
struct MCMF
{
int n, m;
vector<Edge> edges;
vector<int> G[maxn];
int inq[maxn];
int d[maxn];
int p[maxn];
int a[maxn];
void init(int n)
{
this->n = n;
for (int i = 0; i < n; ++i)
{
G[i].clear();
}
edges.clear();
}
void AddEdge(int from, int to, int cap, int cost)
{
edges.push_back(Edge(from, to, cap, 0, cost));
edges.push_back(Edge(to, from, 0, 0, -cost));
m = edges.size();
G[from].push_back(m - 2);
G[to].push_back(m - 1);
}
bool BellmanFord(int s, int t, int & cost)
{
for (int i = 0; i < n; ++i)
{
d[i] = INF;
}
memset(inq, 0, sizeof(inq));
d[s] = 0;
inq[s] = 1;
p[s] = 0;
a[s] = INF;
queue<int> Q;
Q.push(s);
while (!Q.empty())
{
int u = Q.front();
Q.pop();
inq[u] = 0;
for (int i = 0; i < G[u].size(); ++i)
{
Edge & e = edges[G[u][i]];
if (e.cap > e.flow && d[e.to] > d[u] + e.cost)
{
d[e.to] = d[u] + e.cost;
p[e.to] = G[u][i];
a[e.to] = min(a[u], e.cap - e.flow);
if (!inq[e.to])
{
Q.push(e.to);
inq[e.to] = 1;
}
}
}
}
if (d[t] == INF)
{
return false;
}
cost += d[t] * a[t];
for (int u = t; u != s; u = edges[p[u]].from)
{
edges[p[u]].flow += a[t];
edges[p[u] ^ 1].flow -= a[t];
}
return true;
}
int MincostMaxflow(int s, int t)
{
int cost = 0;
while (BellmanFord(s, t, cost));
return cost;
}
};
char s[50][51];
int rid[50][50];
int cid[50][50];
int rcnt, ccnt;
int r[2500], c[2500];
int main()
{
int n, k;
scanf("%d %d", &n, &k);
for (int i = 0; i < n; ++i)
scanf("%s", s[i]);
for (int i = 0; i < n; ++i)
for (int j = 0; j < n; ++j)
{
if (s[i][j] == '#')
continue;
if (!rid[i][j])
{
++rcnt;
int t = j;
while (t < n && s[i][t] == '.')
{
rid[i][t] = rcnt;
++r[rcnt];
++t;
}
}
if (!cid[i][j])
{
++ccnt;
int t = i;
while (t < n && s[t][j] == '.')
{
cid[t][j] = ccnt;
++c[ccnt];
++t;
}
}
}
MCMF mcmf;
mcmf.init(rcnt + ccnt + 3);
for (int i = 1; i <= rcnt; ++i)
for (int j = 0; j < r[i]; ++j)
mcmf.AddEdge(0, i, 1, j);
for (int i = 1; i <= ccnt; ++i)
for (int j = 0; j < c[i]; ++j)
mcmf.AddEdge(rcnt + i, rcnt + ccnt + 1, 1, j);
for (int i = 0; i < n; ++i)
for (int j = 0; j < n; ++j)
{
if (s[i][j] == '#')
continue;
mcmf.AddEdge(rid[i][j], rcnt + cid[i][j], 1, 0);
}
mcmf.AddEdge(rcnt + ccnt + 2, 0, k, 0);
printf("%dn", mcmf.MincostMaxflow(rcnt + ccnt + 2, rcnt + ccnt + 1));
return 0;
}
Problem solution in C.
#include<stdio.h>
#include<stdbool.h>
#define maxn 155
#define maxV 24035
#define maxE 96110
bool area[maxn][maxn];
int hnum[maxn][maxn], vnum[maxn][maxn], vdeg[maxn*maxn], hdeg[maxn*maxn], first[maxV], next[maxE], to[maxE], from[maxE], cap[maxE], cost[maxE], ecnt;
void add_edge(int u, int v, int _cap, int _cost)
{
next[ecnt] = first[u];
to[ecnt] = v;
from[ecnt] = u;
cap[ecnt] = _cap;
cost[ecnt] = _cost;
first[u] = ecnt;
ecnt++;
next[ecnt] = first[v];
to[ecnt] = u;
from[ecnt] = v;
cap[ecnt] = 0;
cost[ecnt] = -_cost;
first[v] = ecnt;
ecnt++;
}
bool inq[maxV];
int q[maxV], dist[maxV], h[maxV];
int push_flow(int S, int T)
{
for( int i = 0 ; i <= T ; i++ )
{
inq[i] = 0, dist[i] = (int)1e9, h[i] = -1;
}
int ql = 0, qr = 0;
dist[S] = 0;
h[S] = -1;
q[qr++] = S;
inq[S] = 1;
while( ql != qr )
{
int cur = q[ql];
inq[cur] = 0;
ql++;
if( ql == maxV )
{
ql = 0;
}
for( int i = first[cur] ; i != -1 ; i = next[i] )
{
if( cap[i] > 0 && dist[to[i]] > dist[cur] + cost[i] )
{
dist[to[i]] = dist[cur] + cost[i];
h[to[i]] = i;
if(!inq[to[i]])
{
q[qr] = to[i];
inq[to[i]] = 1;
qr++;
if( qr == maxV )
{
qr = 0;
}
}
}
}
}
if( dist[T] == (int)1e9 )
{
return -1;
}
int cur = T, pcost = 0;
while( h[cur] != -1 )
{
cap[h[cur]]--;
cap[h[cur]^1]++;
pcost += cost[h[cur]];
cur = from[h[cur]];
}
return pcost;
}
int main()
{
int n, k;
scanf("%d%d", &n, &k);
for( int i = 0 ; i < n ; i++ )
{
for( int j = 0 ; j < n ; j++ )
{
char u[3];
scanf("%1s", u);
if( u[0] == '#' )
{
area[i][j] = 0;
}
else
{
area[i][j] = 1;
}
}
}
int hcnt = 0, vcnt = 0;
for( int i = 0 ; i < n ; i++ )
{
for( int j = 0 ; j < n ; j++ )
{
if(area[i][j])
{
if( j == 0 || !area[i][j-1] )
{
hnum[i][j] = hcnt++;
}
else
{
hnum[i][j] = hnum[i][j-1];
}
}
}
}
for( int j = 0 ; j < n ; j++ )
{
for( int i = 0 ; i < n ; i++ )
{
if(area[i][j])
{
if( i == 0 || !area[i-1][j] )
{
vnum[i][j] = vcnt++;
}
else
{
vnum[i][j] = vnum[i-1][j];
}
}
}
}
int S = hcnt + vcnt, T = hcnt + vcnt + 1;
ecnt = 0;
for( int i = 0 ; i < hcnt ; i++ )
{
hdeg[i] = 0;
}
for( int i = 0 ; i < vcnt ; i++ )
{
vdeg[i] = 0;
}
for( int i = 0 ; i < n ; i++ )
{
for( int j = 0 ; j < n ; j++ )
{
if(area[i][j])
{
hdeg[hnum[i][j]]++, vdeg[vnum[i][j]]++;
}
}
}
for( int i = 0 ; i <= T ; i++ )
{
first[i] = -1;
}
for( int i = 0 ; i < hcnt ; i++ )
{
for( int j = 0 ; j < hdeg[i] ; j++ )
{
add_edge(S, i, 1, j);
}
}
for( int i = 0 ; i < vcnt ; i++ )
{
for( int j = 0 ; j < vdeg[i] ; j++ )
{
add_edge(i+hcnt, T, 1, j);
}
}
for( int i = 0 ; i < n ; i++ )
{
for( int j = 0 ; j < n ; j++ )
{
if(area[i][j])
{
add_edge(hnum[i][j], vnum[i][j] + hcnt, 1, 0);
}
}
}
int res = 0;
for( int i = 0 ; i < k ; i++ )
{
int z = push_flow(S, T);
res += z;
}
printf("%d", res);
return 0;
}
