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/rust/chapter_searching/two_sum.rs

@@ -11,7 +11,7 @@ use std::collections::HashMap;
 /* 方法一：暴力枚举 */
 pub fn two_sum_brute_force(nums: &Vec<i32>, target: i32) -> Option<Vec<i32>> {
     let size = nums.len();
-    // 两层循环，时间复杂度 O(n^2)
+    // 两层循环，时间复杂度为 O(n^2)
     for i in 0..size - 1 {
         for j in i + 1..size {
             if nums[i] + nums[j] == target {
@@ -24,9 +24,9 @@ pub fn two_sum_brute_force(nums: &Vec<i32>, target: i32) -> Option<Vec<i32>> {
 
 /* 方法二：辅助哈希表 */
 pub fn two_sum_hash_table(nums: &Vec<i32>, target: i32) -> Option<Vec<i32>> {
-    // 辅助哈希表，空间复杂度 O(n)
+    // 辅助哈希表，空间复杂度为 O(n)
     let mut dic = HashMap::new();
-    // 单层循环，时间复杂度 O(n)
+    // 单层循环，时间复杂度为 O(n)
     for (i, num) in nums.iter().enumerate() {
         match dic.get(&(target - num)) {
             Some(v) => return Some(vec![*v as i32, i as i32]),