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add 51. golang
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‎README.md

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|048|Rotate Image|[Golang](https://github.com/zj972/leetcode/tree/master/code/048.%20Rotate%20Image)|Medium|
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|049|Group Anagrams|[Golang](https://github.com/zj972/leetcode/tree/master/code/049.%20Group%20Anagrams)|Medium|
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|050|Pow(x, n)|[Golang](https://github.com/zj972/leetcode/tree/master/code/050.%20Pow(x%2C%20n))|Medium|
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|051|N-Queens|[Golang](https://github.com/zj972/leetcode/tree/master/code/051.%20N-Queens)|Hard|
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|058|Length of Last Word|[JavaScript](https://github.com/zj972/leetcode/tree/master/code/058.%20Length%20of%20Last%20Word)|Easy|
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|062|Unique Paths|[JavaScript](https://github.com/zj972/leetcode/tree/master/code/062.%20Unique%20Paths)|Medium|
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|066|Plus One|[JavaScript](https://github.com/zj972/leetcode/tree/master/code/066.%20Plus%20One)|Easy|

‎code/051. N-Queens/README.md

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# 51. N-Queens
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The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.
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![img](https://leetcode.com/static/images/problemset/8-queens.png)
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Given an integer n, return all distinct solutions to the n-queens puzzle.
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Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space respectively.
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##### Example:
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Input: 4
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```text
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Output: [
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[".Q..", // Solution 1
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"...Q",
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"Q...",
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"..Q."],
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["..Q.", // Solution 2
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"Q...",
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"...Q",
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".Q.."]
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]
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```
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Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above.
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n 皇后问题研究的是如何将 n 个皇后放置在 n×n 的棋盘上，并且使皇后彼此之间不能相互攻击。
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![img](https://leetcode.com/static/images/problemset/8-queens.png)
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上图为 8 皇后问题的一种解法。
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给定一个整数 n，返回所有不同的 n 皇后问题的解决方案。
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每一种解法包含一个明确的 n 皇后问题的棋子放置方案，该方案中 'Q' 和 '.' 分别代表了皇后和空位。
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##### 示例:
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输入: 4
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```text
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输出: [
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[".Q..", // 解法 1
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"...Q",
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"Q...",
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"..Q."],
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["..Q.", // 解法 2
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"Q...",
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"...Q",
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".Q.."]
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]
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```
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解释: 4 皇后问题存在两个不同的解法。

‎code/051. N-Queens/main.go

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package main
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import (
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"fmt"
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)
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//. 46
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//Q 81
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//Runtime: 56 ms, faster than 18.52% of Go online submissions for N-Queens.
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//func solveNQueens(n int) [][]string {
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// ret := [][]string{}
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// tmp := make([][]uint8, n)
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// row := make([]bool, n)
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// for i := 0; i < n; i++ {
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// tmp[i] = make([]uint8, n)
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// for j := 0; j < n; j++ {
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// tmp[i][j] = 46
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// }
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// row[i] = true
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// }
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//
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// lBias := make([]bool, 2*n-1)
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// rBias := make([]bool, 2*n-1)
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// for i := 0; i < 2*n-1; i++ {
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// lBias[i] = true
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// rBias[i] = true
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// }
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//
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// addQ(tmp, 0, 0, row, lBias, rBias, &ret, false)
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// return ret
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//}
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//
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//func addQ(data [][]uint8, x int, y int, row []bool, lBias []bool, rBias []bool, ret *[][]string, back bool) {
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// fmt.Printf("data: %v, x: %v, y: %v, row: %v, lBias: %v, rBias: %v\n", data, x, y, row, lBias, rBias)
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// //校验当前位置是否可以插入Q
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// if back {
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// //最上面回滚，结束
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// if x == 0 {
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// return
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// }
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// i := 0
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// for ; i < len(data); i++ {
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// if data[x-1][i] == 81 {
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// data[x-1][i] = 46
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// setCheck(x-1, i, row, lBias, rBias, true)
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// break
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// }
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// }
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// if i == len(data)-1 {
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// addQ(data, x-1, i, row, lBias, rBias, ret, true)
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// } else {
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// addQ(data, x-1, i+1, row, lBias, rBias, ret, false)
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// }
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// } else {
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// if row[y] && lBias[x+y] && rBias[(len(rBias)-1)/2+x-y] {
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// data[x][y] = 81
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// if x == len(data)-1 {
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// tmp := []string{}
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// for i := 0; i < len(data); i++ {
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// tmp = append(tmp, string(data[i]))
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// }
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// *ret = append(*ret, tmp)
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//
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// data[x][y] = 46
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// addQ(data, x, y, row, lBias, rBias, ret, true)
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// } else {
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// setCheck(x, y, row, lBias, rBias, false)
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// addQ(data, x+1, 0, row, lBias, rBias, ret, false)
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// }
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// } else {
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// if y+1 < len(data) {
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// addQ(data, x, y+1, row, lBias, rBias, ret, false)
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// } else {
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// addQ(data, x, y, row, lBias, rBias, ret, true)
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// }
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// }
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// }
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//}
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//
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//func setCheck(x int, y int, row []bool, lBias []bool, rBias []bool, key bool) {
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// row[y] = key
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// lBias[x+y] = key
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// rBias[(len(rBias)-1)/2+x-y] = key
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//}
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//Runtime: 8 ms, faster than 100.00% of Go online submissions for N-Queens.
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func solveNQueens(n int) [][]string {
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return dfs(nil, nil, n)
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}
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func dfs(solutions [][]string, xs []int, n int) [][]string {
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qy := len(xs)
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if qy == n {
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return append(solutions, solution(xs, n))
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}
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qx:
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for qx := 0; qx < n; qx++ {
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for y, x := range xs {
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if x == qx || qy-y == x-qx || qy-y == qx-x {
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continue qx
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}
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}
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solutions = dfs(solutions, append(xs, qx), n)
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}
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return solutions
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}
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func solution(xs []int, n int) []string {
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b := make([]byte, n)
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for i := range b {
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b[i] = '.'
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}
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s := make([]string, n)
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for y, x := range xs {
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b[x] = 'Q'
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s[y] = string(b)
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b[x] = '.'
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}
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return s
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}
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func main() {
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fmt.Println(solveNQueens(4))
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}

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