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

View File

@@ -99,6 +99,36 @@ comments: true
return a + b + c # 输出数据
```
=== "Go"
```go title=""
```
=== "JavaScript"
```js title=""
```
=== "TypeScript"
```typescript title=""
```
=== "C"
```c title=""
```
=== "C#"
```csharp title=""
```
## 推算方法
空间复杂度的推算方法和时间复杂度总体类似,只是从统计 “计算操作数量” 变为统计 “使用空间大小” 。与时间复杂度不同的是,**我们一般只关注「最差空间复杂度」**。这是因为内存空间是一个硬性要求,我们必须保证在所有输入数据下都有足够的内存空间预留。
@@ -140,6 +170,36 @@ comments: true
nums = [0] * n # O(n)
```
=== "Go"
```go title=""
```
=== "JavaScript"
```js title=""
```
=== "TypeScript"
```typescript title=""
```
=== "C"
```c title=""
```
=== "C#"
```csharp title=""
```
**在递归函数中,需要注意统计栈帧空间。** 例如函数 `loop()`,在循环中调用了 $n$ 次 `function()` ,每轮中的 `function()` 都返回并释放了栈帧空间,因此空间复杂度仍为 $O(1)$ 。而递归函数 `recur()` 在运行中会同时存在 $n$ 个未返回的 `recur()` ,从而使用 $O(n)$ 的栈帧空间。
=== "Java"
@@ -200,6 +260,36 @@ comments: true
return recur(n - 1)
```
=== "Go"
```go title=""
```
=== "JavaScript"
```js title=""
```
=== "TypeScript"
```typescript title=""
```
=== "C"
```c title=""
```
=== "C#"
```csharp title=""
```
## 常见类型
设输入数据大小为 $n$ ,常见的空间复杂度类型有(从低到高排列)
@@ -284,6 +374,36 @@ $$
function()
```
=== "Go"
```go title="space_complexity_types.go"
```
=== "JavaScript"
```js title="space_complexity_types.js"
```
=== "TypeScript"
```typescript title="space_complexity_types.ts"
```
=== "C"
```c title="space_complexity_types.c"
```
=== "C#"
```csharp title="space_complexity_types.cs"
```
### 线性阶 $O(n)$
线性阶常见于元素数量与 $n$ 成正比的数组、链表、栈、队列等。
@@ -341,6 +461,36 @@ $$
mapp[i] = str(i)
```
=== "Go"
```go title="space_complexity_types.go"
```
=== "JavaScript"
```js title="space_complexity_types.js"
```
=== "TypeScript"
```typescript title="space_complexity_types.ts"
```
=== "C"
```c title="space_complexity_types.c"
```
=== "C#"
```csharp title="space_complexity_types.cs"
```
以下递归函数会同时存在 $n$ 个未返回的 `algorithm()` 函数,使用 $O(n)$ 大小的栈帧空间。
=== "Java"
@@ -375,6 +525,36 @@ $$
linearRecur(n - 1)
```
=== "Go"
```go title="space_complexity_types.go"
```
=== "JavaScript"
```js title="space_complexity_types.js"
```
=== "TypeScript"
```typescript title="space_complexity_types.ts"
```
=== "C"
```c title="space_complexity_types.c"
```
=== "C#"
```csharp title="space_complexity_types.cs"
```
![space_complexity_recursive_linear](space_complexity.assets/space_complexity_recursive_linear.png)
<p align="center"> Fig. 递归函数产生的线性阶空间复杂度 </p>
@@ -428,6 +608,36 @@ $$
num_matrix = [[0] * n for _ in range(n)]
```
=== "Go"
```go title="space_complexity_types.go"
```
=== "JavaScript"
```js title="space_complexity_types.js"
```
=== "TypeScript"
```typescript title="space_complexity_types.ts"
```
=== "C"
```c title="space_complexity_types.c"
```
=== "C#"
```csharp title="space_complexity_types.cs"
```
在以下递归函数中,同时存在 $n$ 个未返回的 `algorihtm()` ,并且每个函数中都初始化了一个数组,长度分别为 $n, n-1, n-2, ..., 2, 1$ ,平均长度为 $\frac{n}{2}$ ,因此总体使用 $O(n^2)$ 空间。
=== "Java"
@@ -465,6 +675,36 @@ $$
return quadratic_recur(n - 1)
```
=== "Go"
```go title="space_complexity_types.go"
```
=== "JavaScript"
```js title="space_complexity_types.js"
```
=== "TypeScript"
```typescript title="space_complexity_types.ts"
```
=== "C"
```c title="space_complexity_types.c"
```
=== "C#"
```csharp title="space_complexity_types.cs"
```
![space_complexity_recursive_quadratic](space_complexity.assets/space_complexity_recursive_quadratic.png)
<p align="center"> Fig. 递归函数产生的平方阶空间复杂度 </p>
@@ -511,6 +751,36 @@ $$
return root
```
=== "Go"
```go title="space_complexity_types.go"
```
=== "JavaScript"
```js title="space_complexity_types.js"
```
=== "TypeScript"
```typescript title="space_complexity_types.ts"
```
=== "C"
```c title="space_complexity_types.c"
```
=== "C#"
```csharp title="space_complexity_types.cs"
```
![space_complexity_exponential](space_complexity.assets/space_complexity_exponential.png)
<p align="center"> Fig. 满二叉树下的指数阶空间复杂度 </p>

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@@ -20,7 +20,7 @@ comments: true
=== "Java"
```java title="" title="leetcode_two_sum.java"
```java title="leetcode_two_sum.java"
class SolutionBruteForce {
public int[] twoSum(int[] nums, int target) {
int size = nums.length;
@@ -85,6 +85,30 @@ comments: true
}
```
=== "JavaScript"
```js title="leetcode_two_sum.js"
```
=== "TypeScript"
```typescript title="leetcode_two_sum.ts"
```
=== "C"
```c title="leetcode_two_sum.c"
```
=== "C#"
```csharp title="leetcode_two_sum.cs"
```
### 方法二:辅助哈希表
时间复杂度 $O(N)$ ,空间复杂度 $O(N)$ ,属于「空间换时间」。
@@ -93,7 +117,7 @@ comments: true
=== "Java"
```java title="" title="leetcode_two_sum.java"
```java title="leetcode_two_sum.java"
class SolutionHashMap {
public int[] twoSum(int[] nums, int target) {
int size = nums.length;
@@ -163,3 +187,27 @@ comments: true
return nil
}
```
=== "JavaScript"
```js title="leetcode_two_sum.js"
```
=== "TypeScript"
```typescript title="leetcode_two_sum.ts"
```
=== "C"
```c title="leetcode_two_sum.c"
```
=== "C#"
```csharp title="leetcode_two_sum.cs"
```

View File

@@ -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。