From a83e44ea6c6b5c2e979ffcb9b4c1c8aa2a942c55 Mon Sep 17 00:00:00 2001
From: Sombit Bose <sombit.bose15@gmail.com>
Date: Wed, 29 Apr 2020 22:11:47 +0530
Subject: [PATCH] Create n_queens_all_solution_optimised.cpp

---
 .../n_queens_all_solution_optimised.cpp       | 86 +++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 backtracking/n_queens_all_solution_optimised.cpp

diff --git a/backtracking/n_queens_all_solution_optimised.cpp b/backtracking/n_queens_all_solution_optimised.cpp
new file mode 100644
index 000000000..f8da31c4f
--- /dev/null
+++ b/backtracking/n_queens_all_solution_optimised.cpp
@@ -0,0 +1,86 @@
+#include <iostream>
+#define n 4
+#define inc_loop(var,start,stop,step) for(int var=start;var<=stop;var+=step)
+#define dec_loop(var,start,stop,step) for(int var=start;var>=stop;var-=step)
+
+void PrintSol(int Board[n][n]) 
+{
+    inc_loop(i,0,n-1,1) 
+    {
+        inc_loop(j,0,n-1,1)
+            std::cout << Board[i][j] << " ";
+        std::cout << std::endl;
+    }
+    std::cout << std::endl;
+    if (n%2==0 || (n%2==1 && Board[n/2+1][0]!=1))
+    {
+        inc_loop(i,0,n-1,1)
+        {
+            dec_loop(j,n-1,0,1)
+                std::cout<<Board[i][j]<<" ";
+            std::cout<<std::endl;
+        }
+        std::cout<<std::endl;
+    }
+}
+
+bool CanIMove(int Board[n][n], int row, int col) {
+    /// check in the row
+    for (int i = 0; i < col; i++) {
+        if (Board[row][i] == 1)
+            return false;
+    }
+    /// check the first diagonal
+    for (int i = row, j = col; i >= 0 && j >= 0; i--, j--) {
+        if (Board[i][j] == 1)
+            return false;
+    }
+    /// check the second diagonal
+    for (int i = row, j = col; i <= n - 1 && j >= 0; i++, j--) {
+        if (Board[i][j] == 1)
+            return false;
+    }
+    return true;
+}
+
+void NQueenSol(int Board[n][n], int col) {
+    if (col >= n) {
+        PrintSol(Board);
+        return;
+    }
+    inc_loop(i,0,n-1,1)
+    {
+        if (CanIMove(Board, i, col)) {
+            Board[i][col] = 1;
+            NQueenSol(Board, col + 1);
+            Board[i][col] = 0;
+        }
+    }
+}
+
+int main() {
+    int Board[n][n] = {0};
+    if (n%2==0)
+    {
+        inc_loop(i,0,n/2-1,1)
+        {
+            if (CanIMove(Board, i, 0)) {
+                Board[i][0] = 1;
+                NQueenSol(Board,1);
+                Board[i][0] = 0;
+            }
+        }
+    }
+    else
+    {
+        inc_loop(i,0,n/2,1)
+        {
+            if (CanIMove(Board, i,0)) {
+                Board[i][0] = 1;
+                NQueenSol(Board,1);
+                Board[i][0] = 0;
+            }
+        }
+    }
+    return 0;
+}