Create nqueens.cpp

Author: avidLearnerInProgress

nqueens.cpp

@@ -0,0 +1,66 @@
+class Solution {
+public:
+    vector<vector<string>>global_result;
+    
+    void printResult(int matrix[][9],int n){
+        vector<string> local_result(n);
+        for(int i=0;i<n;i++) {
+            string tmp=""; // creating a tmp string             
+            for(int j=0;j<n;j++) {
+                if(matrix[i][j]==1) {
+                    tmp+="Q"; // appending the results to the tmp string
+                } else {
+                    tmp+=".";
+                }
+            }
+            local_result[i]=tmp; // putting the final tmp string result into the vector
+        }
+        global_result.push_back(local_result); // inserting the final vector into the resultatnt vector
+    }
+    
+    bool isValid(int matrix[][9],int row,int col,int n) {
+        
+        // col check
+        for(int r=0;r<row;r++) { 
+            if(matrix[r][col]==1) return false;
+        }
+        
+        // left diagonal
+        int i=row,j=col;
+        while(i>=0 && j>=0) {
+            if(matrix[i][j]==1) return false;
+            i--;j--;
+        }
+        
+        // right diagonal 
+        i=row,j=col;
+        while(i>=0 && j<n) {
+            if(matrix[i][j]==1) return false;
+            i--;j++;
+        }
+
+        return true;
+    }
+    
+    bool solve(int matrix[][9],int row,int n){
+        if(row==n) { // if in all the rows, queens are placed, that means we have reached the end, print the Chessboard 
+            printResult(matrix,n);
+            return true;
+        }
+        bool nextQueen=false; // "assuming that next Queen's placement is not decided YET"
+        for(int col=0;col<n;col++) { // moving into all the columns of "row" (look at the solve() func call above)
+            if(isValid(matrix,row,col,n)) { // Checking if we can place the queen at this particularr place
+                matrix[row][col]=1; // if yes, mark it as 1
+                nextQueen = solve(matrix,row+1,n);// now looking for next Queen's placement, moving to the next row and calling this function Recursively.
+                matrix[row][col]=0; //Backtracking
+            }
+        }
+        return nextQueen; // returning the nextQueen's placement decision's to the function that called it RECURSIVELY
+    }
+    vector<vector<string>> solveNQueens(int n) {
+        int matrix[9][9]={0}; // creating an 2d array of 9X9 since that os the max limit
+        solve(matrix,0,n); // solve(matrix,starting row,max rows)
+        return global_result;
+    
+    }
+};