89 lines
1.8 KiB
Java
89 lines
1.8 KiB
Java
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public class MaxFlowPreflowN3 {
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int[][] cap;
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public void init(int nodes) {
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cap = new int[nodes][nodes];
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}
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public void addEdge(int s, int t, int capacity) {
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cap[s][t] = capacity;
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}
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public int maxFlow(int s, int t) {
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int n = cap.length;
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int[] h = new int[n];
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h[s] = n - 1;
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int[] maxh = new int[n];
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int[][] f = new int[n][n];
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int[] e = new int[n];
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for (int i = 0; i < n; ++i) {
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f[s][i] = cap[s][i];
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f[i][s] = -f[s][i];
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e[i] = cap[s][i];
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}
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for (int sz = 0;;) {
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if (sz == 0) {
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for (int i = 0; i < n; ++i)
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if (i != s && i != t && e[i] > 0) {
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if (sz != 0 && h[i] > h[maxh[0]])
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sz = 0;
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maxh[sz++] = i;
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}
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}
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if (sz == 0)
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break;
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while (sz != 0) {
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int i = maxh[sz - 1];
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boolean pushed = false;
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for (int j = 0; j < n && e[i] != 0; ++j) {
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if (h[i] == h[j] + 1 && cap[i][j] - f[i][j] > 0) {
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int df = Math.min(cap[i][j] - f[i][j], e[i]);
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f[i][j] += df;
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f[j][i] -= df;
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e[i] -= df;
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e[j] += df;
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if (e[i] == 0)
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--sz;
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pushed = true;
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}
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}
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if (!pushed) {
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h[i] = Integer.MAX_VALUE;
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for (int j = 0; j < n; ++j)
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if (h[i] > h[j] + 1 && cap[i][j] - f[i][j] > 0)
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h[i] = h[j] + 1;
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if (h[i] > h[maxh[0]]) {
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sz = 0;
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break;
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}
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}
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}
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}
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int flow = 0;
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for (int i = 0; i < n; i++)
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flow += f[s][i];
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return flow;
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}
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// Usage example
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public static void main(String[] args) {
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int[][] capacity = { { 0, 3, 2 }, { 0, 0, 2 }, { 0, 0, 0 } };
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int n = capacity.length;
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MaxFlowPreflowN3 flow = new MaxFlowPreflowN3();
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flow.init(n);
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for (int i = 0; i < n; i++)
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for (int j = 0; j < n; j++)
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if (capacity[i][j] != 0)
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flow.addEdge(i, j, capacity[i][j]);
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System.out.println(4 == flow.maxFlow(0, 2));
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}
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}
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