feat: Revised the book (#978)

* Sync recent changes to the revised Word.

* Revised the preface chapter

* Revised the introduction chapter

* Revised the computation complexity chapter

* Revised the chapter data structure

* Revised the chapter array and linked list

* Revised the chapter stack and queue

* Revised the chapter hashing

* Revised the chapter tree

* Revised the chapter heap

* Revised the chapter graph

* Revised the chapter searching

* Reivised the sorting chapter

* Revised the divide and conquer chapter

* Revised the chapter backtacking

* Revised the DP chapter

* Revised the greedy chapter

* Revised the appendix chapter

* Revised the preface chapter doubly

* Revised the figures

codes/swift/chapter_backtracking/n_queens.swift

@@ -16,7 +16,7 @@ func backtrack(row: Int, n: Int, state: inout [[String]], res: inout [[[String]]
         // 计算该格子对应的主对角线和副对角线
         let diag1 = row - col + n - 1
         let diag2 = row + col
-        // 剪枝：不允许该格子所在列、主对角线、副对角线存在皇后
+        // 剪枝：不允许该格子所在列、主对角线、副对角线上存在皇后
         if !cols[col] && !diags1[diag1] && !diags2[diag2] {
             // 尝试：将皇后放置在该格子
             state[row][col] = "Q"
@@ -39,8 +39,8 @@ 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
     var state = Array(repeating: Array(repeating: "#", count: n), count: n)
     var cols = Array(repeating: false, count: n) // 记录列是否有皇后
-    var diags1 = Array(repeating: false, count: 2 * n - 1) // 记录主对角线是否有皇后
-    var diags2 = Array(repeating: false, count: 2 * n - 1) // 记录副对角线是否有皇后
+    var diags1 = Array(repeating: false, count: 2 * n - 1) // 记录主对角线上是否有皇后
+    var diags2 = Array(repeating: false, count: 2 * n - 1) // 记录副对角线上是否有皇后
     var res: [[[String]]] = []
 
     backtrack(row: 0, n: n, state: &state, res: &res, cols: &cols, diags1: &diags1, diags2: &diags2)