feat(kotlin): Add kotlin code for backtracking chapter (#1088)

* feat(kotlin):new kotlin support files * fix(kotlin): reviewed the formatting, comments and so on. * fix(kotlin): fix the indentation and format * feat(kotlin): Add kotlin code for the backtraking chapter. * fix(kotlin): fix incorrect output of preorder_traversal_iii_template.kt file * fix(kotlin): simplify kotlin codes * fix(kotlin): modify n_queens.kt for consistency.
2026-08-22 08:17:15 +00:00 · 2024-02-21 01:57:41 +08:00
parent e9341c51b5
commit 507357ace1
10 changed files with 603 additions and 0 deletions
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+/**
+ * File: preorder_traversal_iii_template.kt
+ * Created Time: 2024-01-25
+ * Author: curtishd (1023632660@qq.com)
+ */
+
+package chapter_backtracking.preorder_traversal_iii_template
+
+import utils.TreeNode
+import utils.printTree
+import java.util.*
+
+/* 判断当前状态是否为解 */
+fun isSolution(state: List<TreeNode?>): Boolean {
+    return state.isNotEmpty() && state[state.size - 1]?.value == 7
+}
+
+/* 记录解 */
+fun recordSolution(state: MutableList<TreeNode?>?, res: MutableList<List<TreeNode?>?>) {
+    res.add(state?.let { ArrayList(it) })
+}
+
+/* 判断在当前状态下，该选择是否合法 */
+fun isValid(state: List<TreeNode?>?, choice: TreeNode?): Boolean {
+    return choice != null && choice.value != 3
+}
+
+/* 更新状态 */
+fun makeChoice(state: MutableList<TreeNode?>, choice: TreeNode?) {
+    state.add(choice)
+}
+
+/* 恢复状态 */
+fun undoChoice(state: MutableList<TreeNode?>, choice: TreeNode?) {
+    state.removeLast()
+}
+
+/* 回溯算法：例题三 */
+fun backtrack(
+    state: MutableList<TreeNode?>,
+    choices: List<TreeNode?>,
+    res: MutableList<List<TreeNode?>?>
+) {
+    // 检查是否为解
+    if (isSolution(state)) {
+        // 记录解
+        recordSolution(state, res)
+    }
+    // 遍历所有选择
+    for (choice in 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
+            backtrack(state, listOf(choice!!.left, choice.right), res)
+            // 回退：撤销选择，恢复到之前的状态
+            undoChoice(state, choice)
+        }
+    }
+}
+
+/* Driver Code */
+fun main() {
+    val root = TreeNode.listToTree(mutableListOf(1, 7, 3, 4, 5, 6, 7))
+    println("\n初始化二叉树")
+    printTree(root)
+
+    // 回溯算法
+    val res: MutableList<List<TreeNode?>?> = ArrayList()
+    backtrack(ArrayList(), mutableListOf(root), res)
+
+    println("\n输出所有根节点到节点 7 的路径，要求路径中不包含值为 3 的节点")
+    for (path in res) {
+        val vals = ArrayList<Int>()
+        for (node in path!!) {
+            if (node != null) {
+                vals.add(node.value)
+            }
+        }
+        println(vals)
+    }
+}