From 66f66500eedf893a108a3f94fd19569f5fbbad2b Mon Sep 17 00:00:00 2001
From: hunter129143 <2440617071@qq.com>
Date: Sat, 7 Oct 2023 23:29:22 +0800
Subject: [PATCH] Add New graphtheory Algorithm - Hungarian algorithm in Java

---
 .../graphtheory/HungarianAlgorithm.java       | 80 +++++++++++++++++++
 .../graphtheory/HungarianAlgorithmTest.java   | 49 ++++++++++++
 2 files changed, 129 insertions(+)
 create mode 100644 src/main/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithm.java
 create mode 100644 src/test/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithmTest.java

diff --git a/src/main/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithm.java b/src/main/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithm.java
new file mode 100644
index 000000000..1b50fd22c
--- /dev/null
+++ b/src/main/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithm.java
@@ -0,0 +1,80 @@
+package com.williamfiset.algorithms.graphtheory;
+
+import java.util.Arrays;
+
+public class HungarianAlgorithm {
+  private double[][] weightMatrix;
+  private int numRows;
+  private int numCols;
+  private int[] rowMatches;
+  private int[] colMatches;
+  private boolean[] rowVisited;
+
+  public int[] findMaxWeightMatching(double[][] matrix) {
+    weightMatrix = matrix;
+    numRows = matrix.length;
+    numCols = matrix[0].length;
+    int maxDim = Math.max(numRows, numCols);
+    rowMatches = new int[maxDim];
+    colMatches = new int[maxDim];
+    rowVisited = new boolean[maxDim];
+
+    // Initialize matching array
+    Arrays.fill(rowMatches, -1);
+    Arrays.fill(colMatches, -1);
+
+    // Add virtual vertices to equalize the number of personnel and tasks
+    if (numRows > numCols) {
+      weightMatrix = expandMatrix(matrix, numRows, numRows);
+      numCols = numRows;
+    } else if (numCols > numRows) {
+      weightMatrix = expandMatrix(matrix, numCols, numCols);
+      numRows = numCols;
+    }
+
+    // Find the match with the maximum weight for each row
+    for (int row = 0; row < numRows; row++) {
+      Arrays.fill(rowVisited, false);
+      if (findAugmentingPath(row)) {
+        Arrays.fill(rowVisited, false); // Reset access status
+      }
+    }
+
+    return Arrays.copyOf(rowMatches, numRows);
+  }
+
+  private boolean findAugmentingPath(int row) {
+    if (!rowVisited[row]) {
+      rowVisited[row] = true;
+      for (int col = 0; col < numCols; col++) {
+        if (isMatchValid(row, col)) {
+          // The current match is valid
+          if (colMatches[col] == -1 || findAugmentingPath(colMatches[col])) {
+            // Augmentation path found, update matching
+            rowMatches[row] = col;
+            colMatches[col] = row;
+            return true;
+          }
+        }
+      }
+    }
+    return false;
+  }
+
+  private boolean isMatchValid(int row, int col) {
+    // Check if there are edges in the weight matrix, or modify other conditions as needed
+    return weightMatrix[row][col] > 0;
+  }
+
+  public static double[][] expandMatrix(double[][] matrix, int targetRows, int targetCols) {
+    double[][] expandedMatrix = new double[targetRows][targetCols];
+    for (int row = 0; row < targetRows; row++) {
+      if (row < matrix.length) {
+        System.arraycopy(matrix[row], 0, expandedMatrix[row], 0, matrix[row].length);
+      } else {
+        Arrays.fill(expandedMatrix[row], 0.0);
+      }
+    }
+    return expandedMatrix;
+  }
+}
diff --git a/src/test/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithmTest.java b/src/test/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithmTest.java
new file mode 100644
index 000000000..398c6c11d
--- /dev/null
+++ b/src/test/java/com/williamfiset/algorithms/graphtheory/HungarianAlgorithmTest.java
@@ -0,0 +1,49 @@
+package com.williamfiset.algorithms.graphtheory;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import java.util.*;
+import org.junit.jupiter.api.*;
+
+class HungarianAlgorithmTest {
+
+  @Test
+  void findMaxWeightMatching() {
+    HungarianAlgorithm hungarianAlgorithm = new HungarianAlgorithm();
+
+    double[][] matrix = {
+      {1, 2, 3},
+      {4, 5, 6},
+      {7, 8, 9}
+    };
+
+    int[] matching = hungarianAlgorithm.findMaxWeightMatching(matrix);
+
+    int[] expectedMatching = {2, 1, 0};
+
+    assertThat(matching).isEqualTo(expectedMatching);
+  }
+
+  @Test
+  void expandMatrix() {
+    HungarianAlgorithm hungarianAlgorithm = new HungarianAlgorithm();
+
+    double[][] matrix = {
+      {1, 2},
+      {3, 4}
+    };
+
+    int targetRows = 3;
+    int targetCols = 3;
+
+    double[][] expandedMatrix = hungarianAlgorithm.expandMatrix(matrix, targetRows, targetCols);
+
+    double[][] expectedMatrix = {
+      {1, 2, 0},
+      {3, 4, 0},
+      {0, 0, 0}
+    };
+
+    assertThat(expandedMatrix).isEqualTo(expectedMatrix);
+  }
+}