87 lines
1.7 KiB
Java
87 lines
1.7 KiB
Java
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public class MaxFlowPreflowN4 {
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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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void push(int u, int v, int[][] f, int[] e, int[][] c) {
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int d = Math.min(e[u], c[u][v] - f[u][v]);
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f[u][v] += d;
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f[v][u] = -f[u][v];
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e[u] -= d;
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e[v] += d;
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}
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void lift(int u, int[] h, int[][] f, int[][] c) {
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int d = Integer.MAX_VALUE;
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for (int i = 0; i < f.length; i++)
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if (c[u][i] - f[u][i] > 0)
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d = Math.min(d, h[i]);
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if (d == Integer.MAX_VALUE)
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return;
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h[u] = d + 1;
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}
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public int maxFlow(int src, int dest) {
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int n = cap.length;
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int[][] f = new int[n][n];
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for (int i = 1; i < n; i++) {
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f[0][i] = cap[0][i];
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f[i][0] = -cap[0][i];
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}
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int[] h = new int[n];
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h[0] = n;
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int[] e = new int[n];
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for (int i = 1; i < n; i++)
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e[i] = f[0][i];
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for (;;) {
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int i;
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for (i = 1; i < n - 1; i++)
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if (e[i] > 0)
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break;
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if (i == n - 1)
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break;
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int j;
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for (j = 0; j < n; j++)
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if (cap[i][j] - f[i][j] > 0 && h[i] == h[j] + 1)
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break;
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if (j < n)
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push(i, j, f, e, cap);
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else
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lift(i, h, f, cap);
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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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if (cap[0][i] != 0)
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flow += f[0][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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MaxFlowPreflowN4 flow = new MaxFlowPreflowN4();
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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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