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.

codes/kotlin/chapter_backtracking/subset_sum_i/subset_sum_i.kt

@@ -0,0 +1,60 @@
+/**
+ * File: subset_sum_i.kt
+ * Created Time: 2024-01-25
+ * Author: curtishd (1023632660@qq.com)
+ */
+
+package chapter_backtracking.subset_sum_i
+
+import java.util.*
+
+/* 回溯算法：子集和 I */
+fun backtrack(
+    state: MutableList<Int>,
+    target: Int,
+    choices: IntArray,
+    start: Int,
+    res: MutableList<List<Int>?>
+) {
+    // 子集和等于 target 时，记录解
+    if (target == 0) {
+        res.add(ArrayList(state))
+        return
+    }
+    // 遍历所有选择
+    // 剪枝二：从 start 开始遍历，避免生成重复子集
+    for (i in start..<choices.size) {
+        // 剪枝一：若子集和超过 target ，则直接结束循环
+        // 这是因为数组已排序，后边元素更大，子集和一定超过 target
+        if (target - choices[i] < 0) {
+            break
+        }
+        // 尝试：做出选择，更新 target, start
+        state.add(choices[i])
+        // 进行下一轮选择
+        backtrack(state, target - choices[i], choices, i, res)
+        // 回退：撤销选择，恢复到之前的状态
+        state.removeAt(state.size - 1)
+    }
+}
+
+/* 求解子集和 I */
+fun subsetSumI(nums: IntArray, target: Int): List<List<Int>?> {
+    val state: MutableList<Int> = ArrayList() // 状态（子集）
+    Arrays.sort(nums) // 对 nums 进行排序
+    val start = 0 // 遍历起始点
+    val res: MutableList<List<Int>?> = ArrayList() // 结果列表（子集列表）
+    backtrack(state, target, nums, start, res)
+    return res
+}
+
+/* Driver Code */
+fun main() {
+    val nums = intArrayOf(3, 4, 5)
+    val target = 9
+
+    val res = subsetSumI(nums, target)
+
+    println("输入数组 nums = ${nums.contentToString()}, target = $target")
+    println("所有和等于 $target 的子集 res = $res")
+}