我正在尝试用 Java 实现匈牙利算法。我有一个 NxN 成本矩阵。我正在逐步遵循本指南。所以我有 costMatrix[N][N] 和 2 个数组来跟踪覆盖的行和覆盖的列 - rowCover[N], rowColumn[N] （1 表示已覆盖，0 表示未覆盖）
如何用最少的行数覆盖 0？谁能指出我正确的方向？
任何帮助/建议将不胜感激。
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3 回答
7
检查维基百科文章中算法的第三步（矩阵解释部分），他们解释了一种计算最小行数以覆盖所有 0 的方法
更新：以下是另一种获取覆盖的最小行数的方法0's：
import java.util.ArrayList;
import java.util.List;
public class MinLines {
enum LineType { NONE, HORIZONTAL, VERTICAL }
private static class Line {
int lineIndex;
LineType rowType;
Line(int lineIndex, LineType rowType) {
this.lineIndex = lineIndex;
this.rowType = rowType;
}
LineType getLineType() {
return rowType;
}
int getLineIndex() {
return lineIndex;
}
boolean isHorizontal() {
return rowType == LineType.HORIZONTAL;
}
}
private static boolean isZero(int[] array) {
for (int e : array) {
if (e != 0) {
return false;
}
}
return true;
}
public static List<Line> getMinLines(int[][] matrix) {
if (matrix.length != matrix[0].length) {
throw new IllegalArgumentException("Matrix should be square!");
}
final int SIZE = matrix.length;
int[] zerosPerRow = new int[SIZE];
int[] zerosPerCol = new int[SIZE];
// Count the number of 0's per row and the number of 0's per column
for (int i = 0; i < SIZE; i++) {
for (int j = 0; j < SIZE; j++) {
if (matrix[i][j] == 0) {
zerosPerRow[i]++;
zerosPerCol[j]++;
}
}
}
// There should be at must SIZE lines,
// initialize the list with an initial capacity of SIZE
List<Line> lines = new ArrayList<Line>(SIZE);
LineType lastInsertedLineType = LineType.NONE;
// While there are 0's to count in either rows or colums...
while (!isZero(zerosPerRow) && !isZero(zerosPerCol)) {
// Search the largest count of 0's in both arrays
int max = -1;
Line lineWithMostZeros = null;
for (int i = 0; i < SIZE; i++) {
// If exists another count of 0's equal to "max" but in this one has
// the same direction as the last added line, then replace it with this
//
// The heuristic "fixes" the problem reported by @JustinWyss-Gallifent and @hkrish
if (zerosPerRow[i] > max || (zerosPerRow[i] == max && lastInsertedLineType == LineType.HORIZONTAL)) {
lineWithMostZeros = new Line(i, LineType.HORIZONTAL);
max = zerosPerRow[i];
}
}
for (int i = 0; i < SIZE; i++) {
// Same as above
if (zerosPerCol[i] > max || (zerosPerCol[i] == max && lastInsertedLineType == LineType.VERTICAL)) {
lineWithMostZeros = new Line(i, LineType.VERTICAL);
max = zerosPerCol[i];
}
}
// Delete the 0 count from the line
if (lineWithMostZeros.isHorizontal()) {
zerosPerRow[lineWithMostZeros.getLineIndex()] = 0;
} else {
zerosPerCol[lineWithMostZeros.getLineIndex()] = 0;
}
// Once you've found the line (either horizontal or vertical) with the greater 0's count
// iterate over it's elements and substract the 0's from the other lines
// Example:
// 0's x col:
// [ 0 1 2 3 ] -> 1
// [ 0 2 0 1 ] -> 2
// [ 0 4 3 5 ] -> 1
// [ 0 0 0 7 ] -> 3
// | | | |
// v v v v
// 0's x row: {4} 1 2 0
// [ X 1 2 3 ] -> 0
// [ X 2 0 1 ] -> 1
// [ X 4 3 5 ] -> 0
// [ X 0 0 7 ] -> 2
// | | | |
// v v v v
// {0} 1 2 0
int index = lineWithMostZeros.getLineIndex();
if (lineWithMostZeros.isHorizontal()) {
for (int j = 0; j < SIZE; j++) {
if (matrix[index][j] == 0) {
zerosPerCol[j]--;
}
}
} else {
for (int j = 0; j < SIZE; j++) {
if (matrix[j][index] == 0) {
zerosPerRow[j]--;
}
}
}
// Add the line to the list of lines
lines.add(lineWithMostZeros);
lastInsertedLineType = lineWithMostZeros.getLineType();
}
return lines;
}
public static void main(String... args) {
int[][] example1 =
{
{0, 1, 0, 0, 5},
{1, 0, 3, 4, 5},
{7, 0, 0, 4, 5},
{9, 0, 3, 4, 5},
{3, 0, 3, 4, 5}
};
int[][] example2 =
{
{0, 0, 1, 0},
{0, 1, 1, 0},
{1, 1, 0, 0},
{1, 0, 0, 0},
};
int[][] example3 =
{
{0, 0, 0, 0, 0, 0},
{0, 0, 0, 1, 0, 0},
{0, 0, 1, 1, 0, 0},
{0, 1, 1, 0, 0, 0},
{0, 1, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0}
};
List<int[][]> examples = new ArrayList<int[][]>();
examples.add(example1);
examples.add(example2);
examples.add(example3);
for (int[][] example : examples) {
List<Line> minLines = getMinLines(example);
System.out.printf("Min num of lines for example matrix is: %d\n", minLines.size());
printResult(example, minLines);
System.out.println();
}
}
private static void printResult(int[][] matrix, List<Line> lines) {
if (matrix.length != matrix[0].length) {
throw new IllegalArgumentException("Matrix should be square!");
}
final int SIZE = matrix.length;
System.out.println("Before:");
for (int i = 0; i < SIZE; i++) {
for (int j = 0; j < SIZE; j++) {
System.out.printf("%d ", matrix[i][j]);
}
System.out.println();
}
for (Line line : lines) {
for (int i = 0; i < SIZE; i++) {
int index = line.getLineIndex();
if (line.isHorizontal()) {
matrix[index][i] = matrix[index][i] < 0 ? -3 : -1;
} else {
matrix[i][index] = matrix[i][index] < 0 ? -3 : -2;
}
}
}
System.out.println("\nAfter:");
for (int i = 0; i < SIZE; i++) {
for (int j = 0; j < SIZE; j++) {
System.out.printf("%s ", matrix[i][j] == -1 ? "-" : (matrix[i][j] == -2 ? "|" : (matrix[i][j] == -3 ? "+" : Integer.toString(matrix[i][j]))));
}
System.out.println();
}
}
}
重要的部分是getMinLines方法，它返回一个List包含矩阵0's条目的行。对于示例矩阵打印：
Min num of lines for example matrix is: 3
Before:
0 1 0 0 5
1 0 3 4 5
7 0 0 4 5
9 0 3 4 5
3 0 3 4 5
After:
- + - - -
1 | 3 4 5
- + - - -
9 | 3 4 5
3 | 3 4 5
Min num of lines for example matrix is: 4
Before:
0 0 1 0
0 1 1 0
1 1 0 0
1 0 0 0
After:
| | | |
| | | |
| | | |
| | | |
Min num of lines for example matrix is: 6
Before:
0 0 0 0 0 0
0 0 0 1 0 0
0 0 1 1 0 0
0 1 1 0 0 0
0 1 0 0 0 0
0 0 0 0 0 0
After:
- - - - - -
- - - - - -
- - - - - -
- - - - - -
- - - - - -
- - - - - -
我希望这能给你一个推动，匈牙利算法的其余部分应该不难实现
于 2013-02-10T06:38:46.863 回答
0
我知道这个问题很久以前就已经解决了，但是我想分享我对第 3 步的实现，其中应该以覆盖所有零的方式绘制最小线。
以下是关于我的算法在此步骤中的工作原理的简要说明：
- 在所有单元格上循环，值为零的单元格，我们需要画一条经过它的线，以及它的邻居
- 为了知道应该在哪个方向绘制线，我创建了一个名为 maxVH() 的方法，它将垂直和水平计算零，并返回一个整数。如果整数是正数，画一条垂直线，否则如果为零或负数，画一条水平线。
- colorNeighbors() 方法将绘制线条并计算它们。此外，它会将 1 放在直线垂直通过的元素上。-1 在线条水平通过的元素上。2 在 2 条相交线通过的元素上（水平和垂直）。
使用这 3 种方法的优点是我们知道两次覆盖的元素，我们知道哪些元素被覆盖，哪些没有被覆盖。此外，在绘制线条时，我们会增加线条计数器的数量。
匈牙利算法的完整实现+示例：Github
第 3 步的代码 + 详细注释：
/**
* Step 3.1
* Loop through all elements, and run colorNeighbors when the element visited is equal to zero
* */
public void coverZeros(){
numLines = 0;
lines = new int[values.length][values.length];
for(int row=0; row<values.length;row++){
for(int col=0; col<values.length;col++){
if(values[row][col] == 0)
colorNeighbors(row, col, maxVH(row, col));
}
}
}
/**
* Step 3.2
* Checks which direction (vertical,horizontal) contains more zeros, every time a zero is found vertically, we increment the result
* and every time a zero is found horizontally, we decrement the result. At the end, result will be negative, zero or positive
* @param row Row index for the target cell
* @param col Column index for the target cell
* @return Positive integer means that the line passing by indexes [row][col] should be vertical, Zero or Negative means that the line passing by indexes [row][col] should be horizontal
* */
private int maxVH(int row, int col){
int result = 0;
for(int i=0; i<values.length;i++){
if(values[i][col] == 0)
result++;
if(values[row][i] == 0)
result--;
}
return result;
}
/**
* Step 3.3
* Color the neighbors of the cell at index [row][col]. To know which direction to draw the lines, we pass maxVH value.
* @param row Row index for the target cell
* @param col Column index for the target cell
* @param maxVH Value return by the maxVH method, positive means the line to draw passing by indexes [row][col] is vertical, negative or zero means the line to draw passing by indexes [row][col] is horizontal
* */
private void colorNeighbors(int row, int col, int maxVH){
if(lines[row][col] == 2) // if cell is colored twice before (intersection cell), don't color it again
return;
if(maxVH > 0 && lines[row][col] == 1) // if cell colored vertically and needs to be recolored vertically, don't color it again (Allowing this step, will color the same line (result won't change), but the num of line will be incremented (wrong value for the num of line drawn))
return;
if(maxVH <= 0 && lines[row][col] == -1) // if cell colored horizontally and needs to be recolored horizontally, don't color it again (Allowing this step, will color the same line (result won't change), but the num of line will be incremented (wrong value for the num of line drawn))
return;
for(int i=0; i<values.length;i++){ // Loop on cell at indexes [row][col] and its neighbors
if(maxVH > 0) // if value of maxVH is positive, color vertically
lines[i][col] = lines[i][col] == -1 || lines[i][col] == 2 ? 2 : 1; // if cell was colored before as horizontal (-1), and now needs to be colored vertical (1), so this cell is an intersection (2). Else if this value was not colored before, color it vertically
else // if value of maxVH is zero or negative color horizontally
lines[row][i] = lines[row][i] == 1 || lines[row][i] == 2 ? 2 : -1; // if cell was colored before as vertical (1), and now needs to be colored horizontal (-1), so this cell is an intersection (2). Else if this value was not colored before, color it horizontally
}
// increment line number
numLines++;
// printMatrix(lines); // Monitor the line draw steps
}//End step 3
于 2014-05-05T00:07:25.650 回答
0
这是对@higuaro 答案的改进，但在 Swift 中（适用于
[[0,94,2,91,57,0,115,2,99],[113,19,7,32,42,13,0,35,16],[109,11,31,56,38,29,16,31,0],[81,51,39,0,10,37,24,67,40],[94,0,34,59,23,42,27,30,11],[71,37,39,0,0,47,32,71,48],[71,41,43,4,0,43,28,71,44],[80,110,0,153,137,0,113,0,97],[0,94,0,89,57,8,121,0,105]]
）：
func modifiedGetMinLines(_ matrix: [[Int]]) -> Set<Line> { // O(N^4)
// Using the algorithm found here - https://www.youtube.com/watch?v=rrfFTdO2Z7I
func drawLinesWhileIsolatedZerosExist(_ matrix: inout [[Int]]) -> Set<Line> { // O(N^3)
let N = matrix.count
var lines: Set<Line> = []
var unprocessedTableChange = true
while unprocessedTableChange { // While loop occurs 2N-1 times max!...each time a line in a matrix must be crossed out to continue
unprocessedTableChange = false
for i in 0..<N { // rows
var zeroCount = 0
var columnOfLastZero = -1
for j in 0..<N {
if matrix[i][j] == 0 {
zeroCount += 1
columnOfLastZero = j
}
}
if zeroCount == 1 {
unprocessedTableChange = true
var selectedCol = Line(columnOfLastZero, .VERTICAL)
for i in 0..<N {
if matrix[i][columnOfLastZero] == 0 {
selectedCol.coord.insert(i)
}
matrix[i][columnOfLastZero] = -1 // Cross line out
}
lines.insert(selectedCol)
}
}
for i in 0..<N { // columns
var zeroCount = 0
var rowOfLastZero = -1
for j in 0..<N {
if matrix[j][i] == 0 {
zeroCount += 1
rowOfLastZero = j
}
}
if zeroCount == 1 {
unprocessedTableChange = true
var selectedRow = Line(rowOfLastZero, .HORIZONTAL)
for i in 0..<N {
if matrix[rowOfLastZero][i] == 0 {
selectedRow.coord.insert(i)
}
matrix[rowOfLastZero][i] = -1 // Cross line out
}
lines.insert(selectedRow)
}
}
}
return lines
}
func zerosToProcessExist(_ array: [Int]) -> Bool { // O(N)
for e in array {
if e > 0 { return true }
}
return false
}
var matrix = matrix
let N = matrix.count
var lines: Set<Line> = drawLinesWhileIsolatedZerosExist(&matrix) // O(N^3)
var zerosPerRow = Array(repeating: 0, count: N)
var zerosPerCol = Array(repeating: 0, count: N)
for i in 0..<N { // O(N^2)
for j in 0..<N {
if matrix[i][j] == 0 {
zerosPerRow[i] += 1
zerosPerCol[j] += 1
}
}
}
while zerosToProcessExist(zerosPerRow) || zerosToProcessExist(zerosPerCol) { // While loop occurs 2N-1 times max!...each time a line in a matrix must be crossed out to continue
var max = 0
var lineWithMostZeros: Line?
var linesWithMaxZeros: Set<Line> = []
for i in 0..<N { // O(N)
if zerosPerRow[i] > max {
linesWithMaxZeros = []
linesWithMaxZeros.insert(Line(i, LineType.HORIZONTAL))
max = zerosPerRow[i]
} else if zerosPerRow[i] == max && max > 0 {
linesWithMaxZeros.insert(Line(i, LineType.HORIZONTAL))
}
if zerosPerCol[i] > max {
linesWithMaxZeros = []
linesWithMaxZeros.insert(Line(i, LineType.VERTICAL))
max = zerosPerCol[i]
} else if zerosPerCol[i] == max && max > 0 {
linesWithMaxZeros.insert(Line(i, LineType.VERTICAL))
}
}
if linesWithMaxZeros.count == 1 {
lineWithMostZeros = linesWithMaxZeros.first
} else {
var minScore = Int.max
var minScoreLine: Line?
for l in linesWithMaxZeros {
var score = 0
if l.isHorizontal() {
for j in 0..<N {
if matrix[l.lineIndex][j] == 0 {
for k in 0..<N {
if matrix[k][j] == 0 { score += 1 }
}
}
}
} else {
for j in 0..<N {
if matrix[j][l.lineIndex] == 0 {
for k in 0..<N {
if matrix[j][k] == 0 { score += 1 }
}
}
}
}
if score < minScore {
minScore = score
minScoreLine = l
}
}
lineWithMostZeros = minScoreLine
}
let index = lineWithMostZeros!.lineIndex
var temp: Set<Int> = []
if lineWithMostZeros!.isHorizontal() { // O(N)
zerosPerRow[index] = 0
for j in 0..<N {
if matrix[index][j] == 0 {
zerosPerCol[j] -= 1
temp.insert(j)
}
matrix[index][j] = -1
}
} else {
zerosPerCol[index] = 0
for j in 0..<N {
if matrix[j][index] == 0 {
zerosPerRow[j] -= 1
temp.insert(j)
}
matrix[j][index] = -1
}
}
lineWithMostZeros!.coord = temp
lines.insert(lineWithMostZeros!)
}
return lines
}
于 2021-06-18T01:48:40.277 回答