组合生成

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// 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