finish problem 51

Author: aQua

Diff for: Algorithms/0051.n-queens/README.md

@@ -28,8 +28,9 @@ There exist two distinct solutions to the 4-queens puzzle:
 题目要求，在以下地方都没有其他的Queen
 1. 所在的行
 1. 所在的列
-1. 45度对角线上
+1. 两条45度对角线上
 
+和前面的数独问题一样的解题思路
 ## 总结
 
 

Diff for: Algorithms/0051.n-queens/n-queens.go

@@ -4,23 +4,33 @@ func solveNQueens(n int) [][]string {
 	if n == 0 {
 		return [][]string{}
 	}
+
 	cols := make([]bool, n)
+	// 记录 '\' 方向的对角线的占用情况
 	d1 := make([]bool, 2*n)
+	// 记录 '/' 方向的对角线的占用情况
 	d2 := make([]bool, 2*n)
+
 	board := make([]string, n)
+
 	res := [][]string{}
+
 	dfs(0, cols, d1, d2, board, &res)
+
 	return res
 }
 
-func dfs(r int, cols []bool, d1 []bool, d2 []bool, board []string, res *[][]string) {
+func dfs(r int, cols, d1, d2 []bool, board []string, res *[][]string) {
+
 	if r == len(board) {
 		tmp := make([]string, len(board))
 		copy(tmp, board)
 		*res = append(*res, tmp)
 		return
 	}
+
 	n := len(board)
+
 	for c := 0; c < len(board); c++ {
 		id1 := r - c + n
 		id2 := 2*n - r - c - 1
@@ -31,8 +41,12 @@ func dfs(r int, cols []bool, d1 []bool, d2 []bool, board []string, res *[][]stri
 			}
 			b[c] = 'Q'
 			board[r] = string(b)
+			// 标记占用
 			cols[c], d1[id1], d2[id2] = true, true, true
+
 			dfs(r+1, cols, d1, d2, board, res)
+
+			// 解除标记
 			cols[c], d1[id1], d2[id2] = false, false, false
 		}
 	}

Diff for: Algorithms/0051.n-queens/n-queens_test.go

@@ -28,6 +28,10 @@ func Test_Problem0051(t *testing.T) {
 	ast := assert.New(t)
 
 	qs := []question{
+		question{
+			para{0},
+			ans{[][]string{}},
+		},
 
 		question{
 			para{4},