Fix iiitv#535: Add Backtracking algorithm (N-Queen Problem) [Go] (iii…

…tv#536)

* n queen solution in golang added

* set n value by default

* variables renamed

README.md

@@ -37,7 +37,7 @@ Community (college) maintained list of Algorithms and Data Structures implementa
 | [Longest Palindromic Substring](http://www.geeksforgeeks.org/longest-palindrome-substring-set-1/) | | [:white_check_mark:](longest_palindromic_substring/longest_palindromic_substring.cpp) | [:white_check_mark:](longest_palindromic_substring/LongestPalindromicSubstring.java) | [:white_check_mark:](longest_palindromic_substring/longest_palindromic_substring.py) | | [:white_check_mark:](longest_palindromic_substring/longestPalindromicSubstring.js) | |
 | [Merge Sort](https://www.khanacademy.org/computing/computer-science/algorithms/merge-sort/a/overview-of-merge-sort) | [:white_check_mark:](merge_sort/merge_sort.c) | | [:white_check_mark:](merge_sort/MergeSort.java) | [:white_check_mark:](merge_sort/merge_sort.py) | [:white_check_mark:](merge_sort/merge_sort.go) | [:white_check_mark:](merge_sort/mergeSort.js) | [:white_check_mark:](merge_sort/MergeSort.cs) |
 | [Modular Exponential](http://www.geeksforgeeks.org/modular-exponentiation-power-in-modular-arithmetic/) | [:white_check_mark:](modular_exponential/modular_exponential.c) | | [:white_check_mark:](modular_exponential/ModularExponential.java) | [:white_check_mark:](modular_exponential/modular_exponential.py) | [:white_check_mark:](modular_exponential/modular_exponential.go) | [:white_check_mark:](modular_exponential/modularExponential.js) | |
-| [N-Queen Problem](https://en.wikipedia.org/wiki/Eight_queens_puzzle) | | [:white_check_mark:](n_queen_problem/NQueenProblem.cpp) | [:white_check_mark:](n_queen_problem/NQueenProblem.java) | [:white_check_mark:](n_queen_problem/n_queen_problem.py) | | | |
+| [N-Queen Problem](https://en.wikipedia.org/wiki/Eight_queens_puzzle) | | [:white_check_mark:](n_queen_problem/NQueenProblem.cpp) | [:white_check_mark:](n_queen_problem/NQueenProblem.java) | [:white_check_mark:](n_queen_problem/n_queen_problem.py) | [:white_check_mark:](n_queen_problem/n_queen_problem.go) | | |
 | [Prime Factor](https://en.wikipedia.org/wiki/Prime_factor) | [:white_check_mark:](prime_factor/prime_factor.c) | | [:white_check_mark:](prime_factor/PrimeFactor.java) | [:white_check_mark:](prime_factor/prime_factor.py) | [:white_check_mark:](prime_factor/prime_factor.go) | [:white_check_mark:](prime_factor/primeFactor.js) | |
 | [Prims](https://en.wikipedia.org/wiki/Prim%27s_algorithm) | [:white_check_mark:](prims/prims.c) | | [:white_check_mark:](prims/Prims.java) | | | [:white_check_mark:](prims/prims.js) | |
 | [Quick Select](https://en.wikipedia.org/wiki/Quickselect) | [:white_check_mark:](quick_select/quick_select.c) | | [:white_check_mark:](quick_select/QuickSelect.java) | [:white_check_mark:](quick_select/quick_select.py) | | | |

n_queen_problem/n_queen_problem.go

@@ -0,0 +1,68 @@
+// Given a chess board having N×N cells
+// place N queens on the board in such a way that no queen attacks any other queen.
+
+// There can be a number of possible solutions for a given length of board.
+// This implementation prints only one valid solution, it can be extended to print all possible valid solutions.
+
+package main
+
+import "fmt"
+
+func main() {
+	boardSize := 8 // size of chess board (8 x 8)
+
+	// make board
+	board := make([][]int, boardSize)
+	for i := range board {
+		board[i] = make([]int, boardSize)
+	}
+
+	if PlaceQueen(&board, boardSize) {
+		for i := 0; i < boardSize; i++ {
+			for j := 0; j < boardSize; j++ {
+				fmt.Printf("%d ", board[i][j])
+			}
+			fmt.Print("\n")
+		}
+	} else {
+		fmt.Println("Not possible")
+	}
+}
+
+func isAttacked(board *[][]int, x, y, boardSize int) bool {
+	for i := 0; i < boardSize; i++ {
+		if (*board)[x][i] == 1 {
+			return true
+		}
+		if (*board)[i][y] == 1 {
+			return true
+		}
+		for j := 0; j < boardSize; j++ {
+			if (i-j == x-y) || (i+j == x+y) {
+				if (*board)[i][j] == 1 {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+// PlaceQueen place queens on the board and will return true if it is possible to place all the queens else false
+func PlaceQueen(board *[][]int, boardSize int) bool {
+	if boardSize == 0 {
+		return true
+	}
+	for i := 0; i < len(*board); i++ {
+		for j := 0; j < len(*board); j++ {
+			if !(isAttacked(board, i, j, len(*board))) {
+				(*board)[i][j] = 1
+				if PlaceQueen(board, boardSize-1) {
+					return true
+				}
+				(*board)[i][j] = 0
+			}
+		}
+	}
+	return false
+}