feat(go/backtracking): add go code (krahets#488)

* feat(go/backtracking): add go code

* feat(backtracking): add n_queens in go

* feat(backtracking): add /preorder_traversal_i_compact in go

* feat(backtracking): add /preorder_traversal_ii_compact in go

* feat(backtracking): add /preorder_traversal_ii_template in go

* feat(backtracking): add preorder_traversal_iii_compact in go

* feat(backtracking): add preorder_traversal_test in go

* feat(backtracking): add permutations_i in go

* feat(backtracking): add permutations_ii in go

* feat(backtracking): add permutation_test in go

* feat(backtracking): fix bug in go

* Update permutations_i.go

---------

Co-authored-by: Yudong Jin <[email protected]>

codes/go/chapter_backtracking/n_queens.go

@@ -0,0 +1,55 @@
+// File: n_queens.go
+// Created Time: 2023-05-09
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+/* 回溯算法：N 皇后 */
+func backtrack(row, n int, state *[][]string, res *[][][]string, cols, diags1, diags2 *[]bool) {
+	// 当放置完所有行时，记录解
+	if row == n {
+		newState := make([][]string, len(*state))
+		for i, _ := range newState {
+			newState[i] = make([]string, len((*state)[0]))
+			copy(newState[i], (*state)[i])
+
+		}
+		*res = append(*res, newState)
+	}
+	// 遍历所有列
+	for col := 0; col < n; col++ {
+		// 计算该格子对应的主对角线和副对角线
+		diag1 := row - col + n - 1
+		diag2 := row + col
+		// 剪枝：不允许该格子所在 (列 或 主对角线 或 副对角线) 包含皇后
+		if !((*cols)[col] || (*diags1)[diag1] || (*diags2)[diag2]) {
+			// 尝试：将皇后放置在该格子
+			(*state)[row][col] = "Q"
+			(*cols)[col], (*diags1)[diag1], (*diags2)[diag2] = true, true, true
+			// 放置下一行
+			backtrack(row+1, n, state, res, cols, diags1, diags2)
+			// 回退：将该格子恢复为空位
+			(*state)[row][col] = "#"
+			(*cols)[col], (*diags1)[diag1], (*diags2)[diag2] = false, false, false
+		}
+	}
+}
+
+func nQueens(n int) [][][]string {
+	// 初始化 n*n 大小的棋盘，其中 'Q' 代表皇后，'#' 代表空位
+	state := make([][]string, n)
+	for i := 0; i < n; i++ {
+		row := make([]string, n)
+		for i := 0; i < n; i++ {
+			row[i] = "#"
+		}
+		state[i] = row
+	}
+	// 记录列是否有皇后
+	cols := make([]bool, n)
+	diags1 := make([]bool, 2*n-1)
+	diags2 := make([]bool, 2*n-1)
+	res := make([][][]string, 0)
+	backtrack(0, n, &state, &res, &cols, &diags1, &diags2)
+	return res
+}

codes/go/chapter_backtracking/n_queens_test.go

@@ -0,0 +1,24 @@
+// File: n_queens_test.go
+// Created Time: 2023-05-14
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestNQueens(t *testing.T) {
+	n := 4
+	res := nQueens(n)
+
+	fmt.Println("输入棋盘长宽为 ", n)
+	fmt.Println("皇后放置方案共有 ", len(res), " 种")
+	for _, state := range res {
+		fmt.Println("--------------------")
+		for _, row := range state {
+			fmt.Println(row)
+		}
+	}
+}

codes/go/chapter_backtracking/permutation_test.go

@@ -0,0 +1,33 @@
+// File: preorder_traversal_i_compact_test.go
+// Created Time: 2023-05-09
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+import (
+	"fmt"
+	"testing"
+
+	. "github.com/krahets/hello-algo/pkg"
+)
+
+func TestPermutationI(t *testing.T) {
+	/* 全排列 I */
+	nums := []int{1, 2, 3}
+	fmt.Printf("输入数组 nums = ")
+	PrintSlice(nums)
+
+	res := permutationsI(nums)
+	fmt.Printf("所有排列 res = ")
+	fmt.Println(res)
+}
+
+func TestPermutationII(t *testing.T) {
+	nums := []int{1, 2, 2}
+	fmt.Printf("输入数组 nums = ")
+	PrintSlice(nums)
+
+	res := permutationsII(nums)
+	fmt.Printf("所有排列 res = ")
+	fmt.Println(res)
+}

codes/go/chapter_backtracking/permutations_i.go

@@ -0,0 +1,38 @@
+// File: permutations_i.go
+// Created Time: 2023-05-14
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+/* 回溯算法：全排列 I */
+func backtrackI(state *[]int, choices *[]int, selected *[]bool, res *[][]int) {
+	// 当状态长度等于元素数量时，记录解
+	if len(*state) == len(*choices) {
+		newState := append([]int{}, *state...)
+		*res = append(*res, newState)
+	}
+	// 遍历所有选择
+	for i := 0; i < len(*choices); i++ {
+		choice := (*choices)[i]
+		// 剪枝：不允许重复选择元素 且 不允许重复选择相等元素
+		if !(*selected)[i] {
+			// 尝试：做出选择，更新状态
+			(*selected)[i] = true
+			*state = append(*state, choice)
+			// 进行下一轮选择
+			backtrackI(state, choices, selected, res)
+			// 回退：撤销选择，恢复到之前的状态
+			(*selected)[i] = false
+			*state = (*state)[:len(*state)-1]
+		}
+	}
+}
+
+/* 全排列 I */
+func permutationsI(nums []int) [][]int {
+	res := make([][]int, 0)
+	state := make([]int, 0)
+	selected := make([]bool, len(nums))
+	backtrackI(&state, &nums, &selected, &res)
+	return res
+}

codes/go/chapter_backtracking/permutations_ii.go

@@ -0,0 +1,45 @@
+// File: permutations_i.go
+// Created Time: 2023-05-14
+// Author: Reanon ([email protected])
+
+// File: permutations_i.go
+// Created Time: 2023-05-14
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+/* 回溯算法：全排列 II */
+func backtrackII(state *[]int, choices *[]int, selected *[]bool, res *[][]int) {
+	// 当状态长度等于元素数量时，记录解
+	if len(*state) == len(*choices) {
+		newState := append([]int{}, *state...)
+		*res = append(*res, newState)
+	}
+	// 遍历所有选择
+	duplicated := make(map[int]struct{}, 0)
+	for i := 0; i < len(*choices); i++ {
+		choice := (*choices)[i]
+		// 剪枝：不允许重复选择元素 且 不允许重复选择相等元素
+		if _, ok := duplicated[choice]; !ok && !(*selected)[i] {
+			// 尝试：做出选择，更新状态
+			// 记录选择过的元素值
+			duplicated[choice] = struct{}{}
+			(*selected)[i] = true
+			*state = append(*state, choice)
+			// 进行下一轮选择
+			backtrackI(state, choices, selected, res)
+			// 回退：撤销选择，恢复到之前的状态
+			(*selected)[i] = false
+			*state = (*state)[:len(*state)-1]
+		}
+	}
+}
+
+/* 全排列 II */
+func permutationsII(nums []int) [][]int {
+	res := make([][]int, 0)
+	state := make([]int, 0)
+	selected := make([]bool, len(nums))
+	backtrackII(&state, &nums, &selected, &res)
+	return res
+}

codes/go/chapter_backtracking/preorder_traversal_i_compact.go

@@ -0,0 +1,22 @@
+// File: preorder_traversal_i_compact.go
+// Created Time: 2023-05-09
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+import (
+	. "github.com/krahets/hello-algo/pkg"
+)
+
+/* 前序遍历：例题一 */
+func preOrderI(root *TreeNode, res *[]*TreeNode) {
+	if root == nil {
+		return
+	}
+	if int(root.Val) == 7 {
+		// 记录解
+		*res = append(*res, root)
+	}
+	preOrderI(root.Left, res)
+	preOrderI(root.Right, res)
+}

codes/go/chapter_backtracking/preorder_traversal_ii_compact.go

@@ -0,0 +1,26 @@
+// File: preorder_traversal_i_compact.go
+// Created Time: 2023-05-09
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+import (
+	. "github.com/krahets/hello-algo/pkg"
+)
+
+/* 前序遍历：例题二 */
+func preOrderII(root *TreeNode, res *[][]*TreeNode, path *[]*TreeNode) {
+	if root == nil {
+		return
+	}
+	// 尝试
+	*path = append(*path, root)
+	if int(root.Val) == 7 {
+		// 记录解
+		*res = append(*res, *path)
+	}
+	preOrderII(root.Left, res, path)
+	preOrderII(root.Right, res, path)
+	// 回退
+	*path = (*path)[:len(*path)-1]
+}

codes/go/chapter_backtracking/preorder_traversal_iii_compact.go

@@ -0,0 +1,27 @@
+// File: preorder_traversal_i_compact.go
+// Created Time: 2023-05-09
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+import (
+	. "github.com/krahets/hello-algo/pkg"
+)
+
+/* 前序遍历：例题三 */
+func preOrderIII(root *TreeNode, res *[][]*TreeNode, path *[]*TreeNode) {
+	// 剪枝
+	if root == nil || root.Val == 3 {
+		return
+	}
+	// 尝试
+	*path = append(*path, root)
+	if int(root.Val) == 7 {
+		// 记录解
+		*res = append(*res, *path)
+	}
+	preOrderIII(root.Left, res, path)
+	preOrderIII(root.Right, res, path)
+	// 回退
+	*path = (*path)[:len(*path)-1]
+}

codes/go/chapter_backtracking/preorder_traversal_iii_template.go

@@ -0,0 +1,58 @@
+// File: preorder_traversal_i_compact.go
+// Created Time: 2023-05-09
+// Author: Reanon ([email protected])
+
+package chapter_backtracking
+
+import (
+	. "github.com/krahets/hello-algo/pkg"
+)
+
+/* 判断当前状态是否为解 */
+func isSolution(state *[]*TreeNode) bool {
+	return len(*state) != 0 && (*state)[len(*state)-1].Val == 7
+}
+
+/* 记录解 */
+func recordSolution(state *[]*TreeNode, res *[][]*TreeNode) {
+	*res = append(*res, *state)
+}
+
+/* 判断在当前状态下，该选择是否合法 */
+func isValid(state *[]*TreeNode, choice *TreeNode) bool {
+	return choice != nil && choice.Val != 3
+}
+
+/* 更新状态 */
+func makeChoice(state *[]*TreeNode, choice *TreeNode) {
+	*state = append(*state, choice)
+}
+
+/* 恢复状态 */
+func undoChoice(state *[]*TreeNode, choice *TreeNode) {
+	*state = (*state)[:len(*state)-1]
+}
+
+/* 回溯算法：例题三 */
+func backtrackIII(state *[]*TreeNode, choices *[]*TreeNode, res *[][]*TreeNode) {
+	// 检查是否为解
+	if isSolution(state) {
+		// 记录解
+		recordSolution(state, res)
+		return
+	}
+	// 遍历所有选择
+	for _, choice := range *choices {
+		// 剪枝：检查选择是否合法
+		if isValid(state, choice) {
+			// 尝试：做出选择，更新状态
+			makeChoice(state, choice)
+			// 进行下一轮选择
+			temp := make([]*TreeNode, 0)
+			temp = append(temp, choice.Left, choice.Right)
+			backtrackIII(state, &temp, res)
+			// 回退：撤销选择，恢复到之前的状态
+			undoChoice(state, choice)
+		}
+	}
+}