组合生成

// C# program to find 
// combinations from n 
// arrays such that one 
// element from each 
// array is present
using System;
using System.Collections.Generic;
class GFG{

// Function to print combinations 
// that contain one element from 
// each of the given arrays
static void print(List<int> []arr)
{
// Number of arrays
int n = arr.Length;

// To keep track of next 
// element in each of 
// the n arrays
int []indices = new int[n];

// Initialize with first 
// element‘s index
for(int i = 0; i < n; i++)
	indices[i] = 0;

while (true)
{
	// Print current combination
	for(int i = 0; i < n; i++)
	Console.Write(arr[i][indices[i]] + " ");
	
	Console.WriteLine();

	// Find the rightmost array 
	// that has more elements 
	// left after the current 
	// element in that array
	int next = n - 1;
	while (next >= 0 && 
		(indices[next] + 1 >= 
		arr[next].Count))
	next--;

	// No such array is found 
	// so no more combinations left
	if (next < 0)
	return;

	// If found move to next 
	// element in that array
	indices[next]++;

	// For all arrays to the right 
	// of this array current index 
	// again points to first element
	for(int i = next + 1; i < n; i++)
	indices[i] = 0;
}
}

// Driver code
public static void Main(String[] args)
{
// Initializing a vector 
// with 3 empty vectors
List<int> []arr = new List<int>[3];
for(int i = 0; i < arr.Length; i++)
	arr[i] = new List<int>();

// Now entering data
// [[1, 2, 3], [4], [5, 6]]
arr[0].Add(1);
arr[0].Add(2);
arr[0].Add(3);
arr[1].Add(4);
arr[2].Add(5);
arr[2].Add(6);

print(arr);
}
}

// This code is contributed by shikhasingrajput