Create code_n-QueenProblem

code_n-QueenProblem

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+#Number of queens
+print ("Enter the number of queens")
+N = int(input())
+
+#chessboard
+#NxN matrix with all elements 0
+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 board[i][k]==1 or 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 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 (board[i][j]!=1):
+                board[i][j] = 1
+                #recursion
+                #wether we can put the next queen with this arrangment or not
+                if N_queen(n-1)==True:
+                    return True
+                board[i][j] = 0
+
+    return False
+
+N_queen(N)
+for i in board:
+    print (i)

solving_sudoku_code

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+SIZE = 9
+#sudoku problem
+#cells with value 0 are vacant cells
+matrix = [
+    [6,5,0,8,7,3,0,9,0],
+    [0,0,3,2,5,0,0,0,8],
+    [9,8,0,1,0,4,3,5,7],
+    [1,0,5,0,0,0,0,0,0],
+    [4,0,0,0,0,0,0,0,2],
+    [0,0,0,0,0,0,5,0,3],
+    [5,7,8,3,0,1,0,2,6],
+    [2,0,0,0,4,8,9,0,0],
+    [0,9,0,6,2,5,0,8,1]]
+
+#function to print sudoku
+def print_sudoku():
+    for i in matrix:
+        print (i)
+
+#function to check if all cells are assigned or not
+#if there is any unassigned cell
+#then this function will change the values of
+#row and col accordingly
+def number_unassigned(row, col):
+    num_unassign = 0
+    for i in range(0,SIZE):
+        for j in range (0,SIZE):
+            #cell is unassigned
+            if matrix[i][j] == 0:
+                row = i
+                col = j
+                num_unassign = 1
+                a = [row, col, num_unassign]
+                return a
+    a = [-1, -1, num_unassign]
+    return a
+#function to check if we can put a
+#value in a paticular cell or not
+def is_safe(n, r, c):
+    #checking in row
+    for i in range(0,SIZE):
+        #there is a cell with same value
+        if matrix[r][i] == n:
+            return False
+    #checking in column
+    for i in range(0,SIZE):
+        #there is a cell with same value
+        if matrix[i][c] == n:
+            return False
+    row_start = (r//3)*3
+    col_start = (c//3)*3;
+    #checking submatrix
+    for i in range(row_start,row_start+3):
+        for j in range(col_start,col_start+3):
+            if matrix[i][j]==n:
+                return False
+    return True
+
+#function to check if we can put a
+#value in a paticular cell or not
+def solve_sudoku():
+    row = 0
+    col = 0
+    #if all cells are assigned then the sudoku is already solved
+    #pass by reference because number_unassigned will change the values of row and col
+    a = number_unassigned(row, col)
+    if a[2] == 0:
+        return True
+    row = a[0]
+    col = a[1]
+    #number between 1 to 9
+    for i in range(1,10):
+        #if we can assign i to the cell or not
+        #the cell is matrix[row][col]
+        if is_safe(i, row, col):
+            matrix[row][col] = i
+            #backtracking
+            if solve_sudoku():
+                return True
+            #f we can't proceed with this solution
+            #reassign the cell
+            matrix[row][col]=0
+    return False
+
+if solve_sudoku():
+    print_sudoku()
+else:
+    print("No solution")