adding working N queens problem solution in C++

cpp/dijkstra_shortest_path.cpp

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+// A C / C++ program for Dijkstra's single source shortest path algorithm.
+// The program is for adjacency matrix representation of the graph
+//
+// http://www.geeksforgeeks.org/greedy-algorithms-set-6-dijkstras-shortest-path-algorithm/
+ 
+#include <stdio.h>
+#include <limits.h>
+ 
+// Number of vertices in the graph
+#define V 9
+ 
+// A utility function to find the vertex with minimum distance value, from
+// the set of vertices not yet included in shortest path tree
+int minDistance(int dist[], bool sptSet[])
+{
+   // Initialize min value
+   int min = INT_MAX, min_index;
+ 
+   for (int v = 0; v < V; v++)
+     if (sptSet[v] == false && dist[v] <= min)
+         min = dist[v], min_index = v;
+ 
+   return min_index;
+}
+ 
+// A utility function to print the constructed distance array
+void printSolution(int dist[], int n)
+{
+   printf("Vertex   Distance from Source\n");
+   for (int i = 0; i < V; i++)
+      printf("%d \t\t %d\n", i, dist[i]);
+}
+ 
+// Funtion that implements Dijkstra's single source shortest path algorithm
+// for a graph represented using adjacency matrix representation
+void dijkstra(int graph[V][V], int src)
+{
+     int dist[V];     // The output array.  dist[i] will hold the shortest
+                      // distance from src to i
+ 
+     bool sptSet[V]; // sptSet[i] will true if vertex i is included in shortest
+                     // path tree or shortest distance from src to i is finalized
+ 
+     // Initialize all distances as INFINITE and stpSet[] as false
+     for (int i = 0; i < V; i++)
+        dist[i] = INT_MAX, sptSet[i] = false;
+ 
+     // Distance of source vertex from itself is always 0
+     dist[src] = 0;
+ 
+     // Find shortest path for all vertices
+     for (int count = 0; count < V-1; count++)
+     {
+       // Pick the minimum distance vertex from the set of vertices not
+       // yet processed. u is always equal to src in first iteration.
+       int u = minDistance(dist, sptSet);
+ 
+       // Mark the picked vertex as processed
+       sptSet[u] = true;
+ 
+       // Update dist value of the adjacent vertices of the picked vertex.
+       for (int v = 0; v < V; v++)
+ 
+         // Update dist[v] only if is not in sptSet, there is an edge from 
+         // u to v, and total weight of path from src to  v through u is 
+         // smaller than current value of dist[v]
+         if (!sptSet[v] && graph[u][v] && dist[u] != INT_MAX 
+                                       && dist[u]+graph[u][v] < dist[v])
+            dist[v] = dist[u] + graph[u][v];
+     }
+ 
+     // print the constructed distance array
+     printSolution(dist, V);
+}
+ 
+// driver program to test above function
+int main()
+{
+   /* Let us create the example graph discussed above */
+   int graph[V][V] = {{0, 4, 0, 0, 0, 0, 0, 8, 0},
+                      {4, 0, 8, 0, 0, 0, 0, 11, 0},
+                      {0, 8, 0, 7, 0, 4, 0, 0, 2},
+                      {0, 0, 7, 0, 9, 14, 0, 0, 0},
+                      {0, 0, 0, 9, 0, 10, 0, 0, 0},
+                      {0, 0, 4, 14, 10, 0, 2, 0, 0},
+                      {0, 0, 0, 0, 0, 2, 0, 1, 6},
+                      {8, 11, 0, 0, 0, 0, 1, 0, 7},
+                      {0, 0, 2, 0, 0, 0, 6, 7, 0}
+                     };
+ 
+    dijkstra(graph, 0);
+ 
+    return 0;
+}

cpp/nqueens.cpp

@@ -0,0 +1,145 @@
+#include <stdio.h>
+#include <iostream>
+#include <vector>
+#include <string.h>
+
+#define NQUEENS 8
+
+using namespace std;
+
+// class with minimal object abstraction
+class Board 
+{
+	public:
+		// make these public so we don't clutter this with accessors. 
+		// verbs, not nouns. simplicity.
+		int size;
+		int* queens; 
+		int* occupiedrows;
+		Board(int board_size) 
+		{
+			// populate stuff
+			this->size = board_size;
+			queens = new int[board_size];
+			occupiedrows = new int[board_size];
+			for(int i=0;i<board_size;i++){
+				queens[i]=0;
+				occupiedrows[i]=0;
+			}
+		};
+		~Board() 
+		{
+			delete [] queens;
+			delete [] occupiedrows;
+		}
+		string toString() 
+		{ 
+			string s = "";
+			s += to_string(this->queens[0]);
+			for(int i=1; i<this->size; i++) { 
+				s += " " + to_string(this->queens[i]);
+			}
+			return s;
+		}
+		void choose(int row, int col) 
+		{
+			if(col < this->size && row < this->size) {
+				this->queens[col] = row;
+				this->occupiedrows[row] = 1;
+			}
+		}
+		void unchoose(int row, int col) 
+		{
+			if(col < this->size && row < this->size) {
+				this->queens[col] = 0;
+				this->occupiedrows[row] = 0;
+			}
+		}
+};
+
+// class that performs minimal amount of wrapping around built-in types 
+
+// SolutionSaver is a static class
+class SolutionSaver
+{
+	private:
+		vector<string> solutions;
+		int nsolutions;
+	public:
+		static SolutionSaver& getInstance()
+		{
+			static SolutionSaver instance;
+			return instance;
+		}
+		void saveSolution(string serialized){
+			solutions.push_back(serialized);
+			nsolutions++;
+		}
+		void printNumSolutions() {
+			cout << nsolutions << endl;
+		}
+		void printSolutions() {
+			for(vector<string>::iterator it = solutions.begin(); it != solutions.end(); it++) {
+				cout << "Solution: " << (*it) << endl;
+			}
+			cout << endl;
+		}
+
+	private:
+		SolutionSaver(){
+			nsolutions = 0;
+		};
+		SolutionSaver(SolutionSaver const&);
+};
+
+
+
+
+void explore(Board* b, int col) 
+{
+	if(col>=b->size) 
+	{ 
+		// Base case
+		SolutionSaver * s = &SolutionSaver::getInstance();
+		s->saveSolution(b->toString());
+	} // Done with base case
+	else 
+	{
+		// Recursive case
+		int size = b->size;
+		int* attacked = new int[size];
+		int* occupied = b->occupiedrows;
+		for(int k=0; k<=(col-1); k++) {
+
+			// attacked on lower right diag
+			int ix1 = b->queens[k] + col - k;
+			if(ix1 >= 0 && ix1 < b->size) {
+				attacked[ix1] = 1;
+			}
+
+			// attacked on upper right diag
+			int ix2 = b->queens[k] - col + k;
+			if(ix2 >= 0 && ix2 < b->size) { 
+				attacked[ix2] = 1;
+			}
+		}
+
+		for(int row=0; row<b->size; row++ ) {
+			if(occupied[row]!=1 && attacked[row]!=1) { 
+				b->choose(row,col);
+				explore(b,col+1);
+				b->unchoose(row,col);
+			}
+		}
+	}// Done with recursive case
+};
+
+
+
+int main(void) 
+{
+	Board b(NQUEENS);
+	explore(&b,0);
+	SolutionSaver * s = &SolutionSaver::getInstance();
+	s->printNumSolutions();
+}