Merge pull request #578 from gauravburjwal/n-queens

added n-queens problem in python

Author: probot-auto-merge[bot]

N-Queens/Python/n-queens.py

@@ -0,0 +1,43 @@
+# Getting number of Queens
+print ("Enter the number of Queens")
+N = int(input())
+
+# Chessboard
+# NxN matrix with all the elements 0
+chess_board = [[0]*N for _ in range(N)]
+
+def is_attack(i, j):
+    # Checking if there is a Queen in row or column
+    for k in range(0,N):
+        if chess_board[i][k]==1 or chess_board[k][j]==1:
+            return True
+    # Checking diagonals
+    for k in range(0,N):
+        for l in range(0,N):
+            if (k+l==i+j) or (k-l==i-j):
+                if chess_board[k][l]==1:
+                    return True
+    return False
+
+def N_queen(n):
+    # If n is 0, solution found
+    if n==0:
+        return True
+    for i in range(0,N):
+        for j in range(0,N):
+            '''Checking if we can place a queen here or not
+            queen will not be placed if the place is being attacked
+            or already occupied'''
+            if (not(is_attack(i,j))) and (chess_board[i][j]!=1):
+                chess_board[i][j] = 1
+                # Recursion
+                # Whether we can put the next Queen with this arrangment or not
+                if N_queen(n-1)==True:
+                    return True
+                chess_board[i][j] = 0
+
+    return False
+
+N_queen(N)
+for i in chess_board:
+    print (i)