Review Swift codes (#1150)

* feat(swift): review for chapter_computational_complexity

* feat(swift): review for chapter_data_structure

* feat(swift): review for chapter_array_and_linkedlist

* feat(swift): review for chapter_stack_and_queue

* feat(swift): review for chapter_hashing

* feat(swift): review for chapter_tree

* feat(swift): add codes for heap article

* feat(swift): review for chapter_heap

* feat(swift): review for chapter_graph

* feat(swift): review for chapter_searching

* feat(swift): review for chapter_sorting

* feat(swift): review for chapter_divide_and_conquer

* feat(swift): review for chapter_backtracking

* feat(swift): review for chapter_dynamic_programming

* feat(swift): review for chapter_greedy

* feat(swift): review for utils

* feat(swift): update ci tool

* feat(swift): trailing closure

* feat(swift): array init

* feat(swift): map index

codes/swift/chapter_backtracking/subset_sum_i.swift

@@ -13,7 +13,7 @@ func backtrack(state: inout [Int], target: Int, choices: [Int], start: Int, res:
     }
     // 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 stride(from: start, to: choices.count, by: 1) {
+    for i in choices.indices.dropFirst(start) {
         // 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 {

codes/swift/chapter_backtracking/subset_sum_i_naive.swift

@@ -12,7 +12,7 @@ func backtrack(state: inout [Int], target: Int, total: Int, choices: [Int], res:
         return
     }
     // 遍历所有选择
-    for i in stride(from: 0, to: choices.count, by: 1) {
+    for i in choices.indices {
         // 剪枝：若子集和超过 target ，则跳过该选择
         if total + choices[i] > target {
             continue

codes/swift/chapter_backtracking/subset_sum_ii.swift

@@ -14,7 +14,7 @@ func backtrack(state: inout [Int], target: Int, choices: [Int], start: Int, res:
     // 遍历所有选择
     // 剪枝二：从 start 开始遍历，避免生成重复子集
     // 剪枝三：从 start 开始遍历，避免重复选择同一元素
-    for i in stride(from: start, to: choices.count, by: 1) {
+    for i in choices.indices.dropFirst(start) {
         // 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 {