Update the codes of backtracking.

codes/cpp/chapter_backtracking/permutations_i.cpp

@@ -21,6 +21,7 @@ void backtrack(vector<int> &state, const vector<int> &choices, vector<bool> &sel
             // 尝试：做出选择，更新状态
             selected[i] = true;
             state.push_back(choice);
+            // 进行下一轮选择
             backtrack(state, choices, selected, res);
             // 回退：撤销选择，恢复到之前的状态
             selected[i] = false;

codes/cpp/chapter_backtracking/permutations_ii.cpp

@@ -23,6 +23,7 @@ void backtrack(vector<int> &state, const vector<int> &choices, vector<bool> &sel
             duplicated.emplace(choice); // 记录选择过的元素值
             selected[i] = true;
             state.push_back(choice);
+            // 进行下一轮选择
             backtrack(state, choices, selected, res);
             // 回退：撤销选择，恢复到之前的状态
             selected[i] = false;

codes/cpp/chapter_backtracking/preorder_traversal_iii_template.cpp

@@ -45,6 +45,7 @@ void backtrack(vector<TreeNode *> &state, vector<TreeNode *> &choices, vector<ve
         if (isValid(state, choice)) {
             // 尝试：做出选择，更新状态
             makeChoice(state, choice);
+            // 进行下一轮选择
             vector<TreeNode *> nextChoices{choice->left, choice->right};
             backtrack(state, nextChoices, res);
             // 回退：撤销选择，恢复到之前的状态

codes/csharp/chapter_backtracking/permutations_i.cs

@@ -25,6 +25,7 @@ public class permutations_i {
                 // 尝试：做出选择，更新状态
                 selected[i] = true;
                 state.Add(choice);
+                // 进行下一轮选择
                 backtrack(state, choices, selected, res);
                 // 回退：撤销选择，恢复到之前的状态
                 selected[i] = false;

codes/csharp/chapter_backtracking/permutations_ii.cs

@@ -27,6 +27,7 @@ public class permutations_ii {
                 duplicated.Add(choice); // 记录选择过的元素值
                 selected[i] = true;
                 state.Add(choice);
+                // 进行下一轮选择
                 backtrack(state, choices, selected, res);
                 // 回退：撤销选择，恢复到之前的状态
                 selected[i] = false;

codes/csharp/chapter_backtracking/preorder_traversal_iii_template.cs

@@ -49,8 +49,8 @@ public class preorder_traversal_iii_template {
             if (isValid(state, choice)) {
                 // 尝试：做出选择，更新状态
                 makeChoice(state, choice);
-                List<TreeNode> nextChoices = new List<TreeNode>() { choice.left, choice.right };
+                // 进行下一轮选择
-                backtrack(state, nextChoices, res);
+                backtrack(state, new List<TreeNode> { choice.left, choice.right }, res);
                 // 回退：撤销选择，恢复到之前的状态
                 undoChoice(state, choice);
             }

codes/java/chapter_backtracking/permutations_i.java

@@ -24,6 +24,7 @@ public class permutations_i {
                 // 尝试：做出选择，更新状态
                 selected[i] = true;
                 state.add(choice);
+                // 进行下一轮选择
                 backtrack(state, choices, selected, res);
                 // 回退：撤销选择，恢复到之前的状态
                 selected[i] = false;

codes/java/chapter_backtracking/permutations_ii.java

@@ -26,6 +26,7 @@ public class permutations_ii {
                 duplicated.add(choice); // 记录选择过的元素值
                 selected[i] = true;
                 state.add(choice);
+                // 进行下一轮选择
                 backtrack(state, choices, selected, res);
                 // 回退：撤销选择，恢复到之前的状态
                 selected[i] = false;

codes/java/chapter_backtracking/preorder_traversal_iii_template.java

@@ -49,6 +49,7 @@ public class preorder_traversal_iii_template {
             if (isValid(state, choice)) {
                 // 尝试：做出选择，更新状态
                 makeChoice(state, choice);
+                // 进行下一轮选择
                 backtrack(state, Arrays.asList(choice.left, choice.right), res);
                 // 回退：撤销选择，恢复到之前的状态
                 undoChoice(state, choice);

codes/python/chapter_backtracking/permutations_i.py

@@ -25,6 +25,7 @@ def backtrack(
             # 尝试：做出选择，更新状态
             selected[i] = True
             state.append(choice)
+            # 进行下一轮选择
             backtrack(state, choices, selected, res)
             # 回退：撤销选择，恢复到之前的状态
             selected[i] = False

codes/python/chapter_backtracking/permutations_ii.py

@@ -27,6 +27,7 @@ def backtrack(
             duplicated.add(choice)  # 记录选择过的元素值
             selected[i] = True
             state.append(choice)
+            # 进行下一轮选择
             backtrack(state, choices, selected, res)
             # 回退：撤销选择，恢复到之前的状态
             selected[i] = False

codes/python/chapter_backtracking/preorder_traversal_iii_template.py

@@ -48,6 +48,7 @@ def backtrack(state: list[TreeNode], choices: list[TreeNode], res: list[list[Tre
         if is_valid(state, choice):
             # 尝试：做出选择，更新状态
             make_choice(state, choice)
+            # 进行下一轮选择
             backtrack(state, [choice.left, choice.right], res)
             # 回退：撤销选择，恢复到之前的状态
             undo_choice(state, choice)