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MaxFlow.java
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205 lines (187 loc) · 5.93 KB
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/**
* @verified https://atcoder.jp/contests/practice2/tasks/practice2_d
*/
class MaxFlow {
public class CapEdge {
private final int from, to;
private long cap;
private final int rev;
CapEdge(int from, int to, long cap, int rev) {
this.from = from;
this.to = to;
this.cap = cap;
this.rev = rev;
}
public int getFrom() {return from;}
public int getTo() {return to;}
public long getCap() {return cap;}
public long getFlow() {return g[to][rev].cap;}
}
private static final long INF = Long.MAX_VALUE;
private final int n;
private int m;
private final java.util.ArrayList<CapEdge> edges;
private final int[] count;
private final CapEdge[][] g;
public MaxFlow(int n) {
this.n = n;
this.edges = new java.util.ArrayList<>();
this.count = new int[n];
this.g = new CapEdge[n][];
}
public int addEdge(int from, int to, long cap) {
rangeCheck(from, 0, n);
rangeCheck(to, 0, n);
nonNegativeCheck(cap, "Capacity");
CapEdge e = new CapEdge(from, to, cap, count[to]);
count[from]++; count[to]++;
edges.add(e);
return m++;
}
public CapEdge getEdge(int i) {
rangeCheck(i, 0, m);
return edges.get(i);
}
public java.util.ArrayList<CapEdge> getEdges() {
return edges;
}
public void changeEdge(int i, long newCap, long newFlow) {
rangeCheck(i, 0, m);
nonNegativeCheck(newCap, "Capacity");
if (newFlow > newCap) {
throw new IllegalArgumentException(
String.format("Flow %d is greater than capacity %d.", newCap, newFlow)
);
}
CapEdge e = edges.get(i);
CapEdge er = g[e.to][e.rev];
e.cap = newCap - newFlow;
er.cap = newFlow;
}
private void buildGraph() {
for (int i = 0; i < n; i++) {
g[i] = new CapEdge[count[i]];
}
int[] idx = new int[n];
for (CapEdge e : edges) {
g[e.to][idx[e.to]++] = new CapEdge(e.to, e.from, 0, idx[e.from]);
g[e.from][idx[e.from]++] = e;
}
}
public long maxFlow(int s, int t) {
return flow(s, t, INF);
}
public long flow(int s, int t, long flowLimit) {
rangeCheck(s, 0, n);
rangeCheck(t, 0, n);
buildGraph();
long flow = 0;
int[] level = new int[n];
int[] que = new int[n];
int[] iter = new int[n];
while (true) {
java.util.Arrays.fill(level, -1);
dinicBFS(s, t, level, que);
if (level[t] < 0) return flow;
java.util.Arrays.fill(iter, 0);
while (true) {
long d = dinicDFS(t, s, flowLimit - flow, iter, level);
if (d <= 0) break;
flow += d;
}
}
}
private void dinicBFS(int s, int t, int[] level, int[] que) {
int hd = 0, tl = 0;
que[tl++] = s;
level[s] = 0;
while (tl > hd) {
int u = que[hd++];
for (CapEdge e : g[u]) {
int v = e.to;
if (e.cap <= 0 || level[v] >= 0) continue;
level[v] = level[u] + 1;
if (v == t) return;
que[tl++] = v;
}
}
}
private long dinicDFS(int cur, int s, long f, int[] iter, int[] level) {
if (cur == s) return f;
long res = 0;
while (iter[cur] < count[cur]) {
CapEdge er = g[cur][iter[cur]++];
int u = er.to;
CapEdge e = g[u][er.rev];
if (level[u] >= level[cur] || e.cap <= 0) continue;
long d = dinicDFS(u, s, Math.min(f - res, e.cap), iter, level);
if (d <= 0) continue;
e.cap -= d;
er.cap += d;
res += d;
if (res == f) break;
}
return res;
}
public long fordFulkersonMaxFlow(int s, int t) {
return fordFulkersonFlow(s, t, INF);
}
public long fordFulkersonFlow(int s, int t, long flowLimit) {
rangeCheck(s, 0, n);
rangeCheck(t, 0, n);
buildGraph();
boolean[] used = new boolean[n];
long flow = 0;
while (true) {
java.util.Arrays.fill(used, false);
long f = fordFulkersonDFS(s, t, flowLimit - flow, used);
if (f <= 0) return flow;
flow += f;
}
}
private long fordFulkersonDFS(int cur, int t, long f, boolean[] used) {
if (cur == t) return f;
used[cur] = true;
for (CapEdge e : g[cur]) {
if (used[e.to] || e.cap <= 0) continue;
long d = fordFulkersonDFS(e.to, t, Math.min(f, e.cap), used);
if (d <= 0) continue;
e.cap -= d;
g[e.to][e.rev].cap += d;
return d;
}
return 0;
}
public boolean[] minCut(int s) {
rangeCheck(s, 0, n);
boolean[] reachable = new boolean[n];
int[] stack = new int[n];
int ptr = 0;
stack[ptr++] = s;
reachable[s] = true;
while (ptr > 0) {
int u = stack[--ptr];
for (CapEdge e : g[u]) {
int v = e.to;
if (reachable[v] || e.cap <= 0) continue;
reachable[v] = true;
stack[ptr++] = v;
}
}
return reachable;
}
private void rangeCheck(int i, int minInlusive, int maxExclusive) {
if (i < 0 || i >= maxExclusive) {
throw new IndexOutOfBoundsException(
String.format("Index %d out of bounds for length %d", i, maxExclusive)
);
}
}
private void nonNegativeCheck(long cap, java.lang.String attribute) {
if (cap < 0) {
throw new IllegalArgumentException(
String.format("%s %d is negative.", attribute, cap)
);
}
}
}