Organizing all the code blocks.

This commit is contained in:
Yudong Jin
2022-12-03 01:31:29 +08:00
parent fec56afd5f
commit 9bd5980a81
21 changed files with 2520 additions and 310 deletions

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@@ -61,6 +61,36 @@ $$
print(0) # 5 ns
```
=== "Go"
```go title=""
```
=== "JavaScript"
```js title=""
```
=== "TypeScript"
```typescript title=""
```
=== "C"
```c title=""
```
=== "C#"
```csharp title=""
```
但实际上, **统计算法的运行时间既不合理也不现实。** 首先,我们不希望预估时间和运行平台绑定,毕竟算法需要跑在各式各样的平台之上。其次,我们很难获知每一种操作的运行时间,这为预估过程带来了极大的难度。
## 统计时间增长趋势
@@ -131,6 +161,36 @@ $$
print(0)
```
=== "Go"
```go title=""
```
=== "JavaScript"
```js title=""
```
=== "TypeScript"
```typescript title=""
```
=== "C"
```c title=""
```
=== "C#"
```csharp title=""
```
![time_complexity_first_example](time_complexity.assets/time_complexity_first_example.png)
<p align="center"> Fig. 算法 A, B, C 的时间增长趋势 </p>
@@ -192,6 +252,36 @@ $$
}
```
=== "Go"
```go title=""
```
=== "JavaScript"
```js title=""
```
=== "TypeScript"
```typescript title=""
```
=== "C"
```c title=""
```
=== "C#"
```csharp title=""
```
$T(n)$ 是个一次函数,说明时间增长趋势是线性的,因此易得时间复杂度是线性阶。
我们将线性阶的时间复杂度记为 $O(n)$ ,这个数学符号被称为「大 $O$ 记号 Big-$O$ Notation」代表函数 $T(n)$ 的「渐进上界 asymptotic upper bound」。
@@ -296,6 +386,36 @@ $$
print(0)
```
=== "Go"
```go title=""
```
=== "JavaScript"
```js title=""
```
=== "TypeScript"
```typescript title=""
```
=== "C"
```c title=""
```
=== "C#"
```csharp title=""
```
### 2. 判断渐进上界
**时间复杂度由多项式 $T(n)$ 中最高阶的项来决定**。这是因为在 $n$ 趋于无穷大时,最高阶的项将处于主导作用,其它项的影响都可以被忽略。
@@ -341,7 +461,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 常数阶 */
int constant(int n) {
int count = 0;
@@ -377,13 +497,43 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
### 线性阶 $O(n)$
线性阶的操作数量相对输入数据大小成线性级别增长。线性阶常出现于单层循环。
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 线性阶 */
int linear(int n) {
int count = 0;
@@ -416,6 +566,36 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
「遍历数组」和「遍历链表」等操作,时间复杂度都为 $O(n)$ ,其中 $n$ 为数组或链表的长度。
!!! tip
@@ -424,7 +604,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 线性阶(遍历数组) */
int arrayTraversal(int[] nums) {
int count = 0;
@@ -462,13 +642,43 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
### 平方阶 $O(n^2)$
平方阶的操作数量相对输入数据大小成平方级别增长。平方阶常出现于嵌套循环,外层循环和内层循环都为 $O(n)$ ,总体为 $O(n^2)$ 。
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 平方阶 */
int quadratic(int n) {
int count = 0;
@@ -511,6 +721,36 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
![time_complexity_constant_linear_quadratic](time_complexity.assets/time_complexity_constant_linear_quadratic.png)
<p align="center"> Fig. 常数阶、线性阶、平方阶的时间复杂度 </p>
@@ -523,7 +763,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 平方阶(冒泡排序) */
int bubbleSort(int[] nums) {
int count = 0; // 计数器
@@ -586,6 +826,36 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
### 指数阶 $O(2^n)$
!!! note
@@ -596,7 +866,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 指数阶(循环实现) */
int exponential(int n) {
int count = 0, base = 1;
@@ -645,6 +915,36 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
![time_complexity_exponential](time_complexity.assets/time_complexity_exponential.png)
<p align="center"> Fig. 指数阶的时间复杂度 </p>
@@ -653,7 +953,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 指数阶(递归实现) */
int expRecur(int n) {
if (n == 1) return 1;
@@ -680,6 +980,36 @@ $$
return exp_recur(n - 1) + exp_recur(n - 1) + 1
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
### 对数阶 $O(\log n)$
对数阶与指数阶正好相反,后者反映 “每轮增加到两倍的情况” ,而前者反映 “每轮缩减到一半的情况” 。对数阶仅次于常数阶,时间增长的很慢,是理想的时间复杂度。
@@ -690,7 +1020,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 对数阶(循环实现) */
int logarithmic(float n) {
int count = 0;
@@ -728,6 +1058,36 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
![time_complexity_logarithmic](time_complexity.assets/time_complexity_logarithmic.png)
<p align="center"> Fig. 对数阶的时间复杂度 </p>
@@ -736,7 +1096,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 对数阶(递归实现) */
int logRecur(float n) {
if (n <= 1) return 0;
@@ -763,6 +1123,36 @@ $$
return log_recur(n / 2) + 1
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
### 线性对数阶 $O(n \log n)$
线性对数阶常出现于嵌套循环中,两层循环的时间复杂度分别为 $O(\log n)$ 和 $O(n)$ 。
@@ -771,7 +1161,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 线性对数阶 */
int linearLogRecur(float n) {
if (n <= 1) return 1;
@@ -812,6 +1202,36 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
![time_complexity_logarithmic_linear](time_complexity.assets/time_complexity_logarithmic_linear.png)
<p align="center"> Fig. 线性对数阶的时间复杂度 </p>
@@ -828,7 +1248,7 @@ $$
=== "Java"
```java title="" title="time_complexity_types.java"
```java title="time_complexity_types.java"
/* 阶乘阶(递归实现) */
int factorialRecur(int n) {
if (n == 0) return 1;
@@ -869,6 +1289,36 @@ $$
return count
```
=== "Go"
```go title="time_complexity_types.go"
```
=== "JavaScript"
```js title="time_complexity_types.js"
```
=== "TypeScript"
```typescript title="time_complexity_types.ts"
```
=== "C"
```c title="time_complexity_types.c"
```
=== "C#"
```csharp title="time_complexity_types.cs"
```
![time_complexity_factorial](time_complexity.assets/time_complexity_factorial.png)
<p align="center"> Fig. 阶乘阶的时间复杂度 </p>
@@ -884,7 +1334,7 @@ $$
=== "Java"
```java title="" title="worst_best_time_complexity.java"
```java title="worst_best_time_complexity.java"
public class worst_best_time_complexity {
/* 生成一个数组,元素为 { 1, 2, ..., n },顺序被打乱 */
static int[] randomNumbers(int n) {
@@ -994,6 +1444,36 @@ $$
print("数字 1 的索引为", index)
```
=== "Go"
```go title="worst_best_time_complexity.go"
```
=== "JavaScript"
```js title="worst_best_time_complexity.js"
```
=== "TypeScript"
```typescript title="worst_best_time_complexity.ts"
```
=== "C"
```c title="worst_best_time_complexity.c"
```
=== "C#"
```csharp title="worst_best_time_complexity.cs"
```
!!! tip
我们在实际应用中很少使用「最佳时间复杂度」,因为往往只有很小概率下才能达到,会带来一定的误导性。反之,「最差时间复杂度」最为实用,因为它给出了一个 “效率安全值” ,让我们可以放心地使用算法。