From 29c5049c7de2d49d43f904ba89bbc9c77d2e9b16 Mon Sep 17 00:00:00 2001
From: xblakicex <xblakicex@outlook.com>
Date: Tue, 10 Jan 2023 22:38:32 +0100
Subject: [PATCH] =?UTF-8?q?=E2=9C=A8=20feat(code):=20add=20rust=20time=5Fc?=
 =?UTF-8?q?omplexity.rs=20example?=
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---
 .../time_complexity.rs                        | 163 ++++++++++++++++++
 1 file changed, 163 insertions(+)
 create mode 100644 codes/rust/chapter_computational_complexity/time_complexity.rs

diff --git a/codes/rust/chapter_computational_complexity/time_complexity.rs b/codes/rust/chapter_computational_complexity/time_complexity.rs
new file mode 100644
index 000000000..a6aa60b31
--- /dev/null
+++ b/codes/rust/chapter_computational_complexity/time_complexity.rs
@@ -0,0 +1,163 @@
+#![allow(unused_variables)]
+
+/* 常数阶 */
+fn constant(n: i32) -> i32 {
+    let mut count = 0;
+    let size = 100000;
+    for _ in 0..size {
+        count += 1
+    }
+    count
+}
+
+fn linear(n: i32) -> i32 {
+    let mut count = 0;
+    for _ in 0..n {
+        count += 1;
+    }
+    count
+}
+
+/* 线性阶（遍历数组） */
+fn array_traversal(nums: &[i32]) -> i32 {
+    let mut count = 0;
+    // 循环次数与数组长度成正比
+    for _ in nums {
+        count += 1;
+    }
+    count
+}
+
+fn quadratic(n: i32) -> i32 {
+    let mut count = 0;
+    // 循环次数与数组长度成平方关系
+    for _ in 0..n {
+        for _ in 0..n {
+            count += 1;
+        }
+    }
+    count
+}
+
+/* 平方阶（冒泡排序） */
+fn bubble_sort(nums: &mut [i32]) -> i32 {
+    let mut count = 0; // 计数器
+    // 外循环：待排序元素数量为 n-1, n-2, ..., 1
+    for i in (1..nums.len()).rev() {
+        // 内循环：冒泡操作
+        for j in 0..i {
+            if nums[j] > nums[j + 1] {
+                // 交换 nums[j] 与 nums[j + 1]
+                let tmp = nums[j];
+                nums[j] = nums[j + 1];
+                nums[j + 1] = tmp;
+                count += 3; // 元素交换包含 3 个单元操作
+            }
+        }
+    }
+    count
+}
+
+/* 指数阶（循环实现） */
+fn exponential(n: i32) -> i32 {
+    let mut count = 0;
+    let mut base = 1;
+    // cell 每轮一分为二，形成数列 1, 2, 4, 8, ..., 2^(n-1)
+    for _ in 0..n {
+        for _ in 0..base {
+            count += 1
+        }
+        base *= 2;
+    }
+    // count = 1 + 2 + 4 + 8 + .. + 2^(n-1) = 2^n - 1
+    count
+}
+
+/* 指数阶（递归实现） */
+fn exp_recur(n: i32) -> i32 {
+    if n == 1 {
+        return 1;
+    }
+    exp_recur(n - 1) + exp_recur(n - 1) + 1
+}
+
+/* 对数阶（循环实现） */
+fn logarithmic(mut n: i32) -> i32 {
+    let mut count = 0;
+
+    while n > 1 {
+        n = n / 2;
+        count += 1;
+    }
+    count
+}
+
+fn log_recur(n: i32) -> i32 {
+    if n <= 1 {
+        return 0;
+    }
+    log_recur(n / 2) + 1
+}
+
+/* 线性对数阶 */
+fn linear_log_recur(n: f64) -> i32 {
+    if n <= 1.0 {
+        return 1;
+    }
+    let mut count = linear_log_recur(n / 2.0) + linear_log_recur(n / 2.0);
+    for _ in 0 ..n as i32 {
+        count += 1;
+    }
+    return count
+}
+
+/* 阶乘阶（递归实现） */
+fn factorial_recur(n: i32) -> i32 {
+    if n == 0 {
+        return 1;
+    }
+    let mut count = 0;
+    // 从 1 个分裂出 n 个
+    for _ in 0..n {
+        count += factorial_recur(n - 1);
+    }
+    count
+}
+
+/* Driver Code */
+fn main() {
+    // 可以修改 n 运行，体会一下各种复杂度的操作数量变化趋势
+    let n: i32 = 8;
+    println!("输入数据大小 n = {}", n);
+
+    let mut count = constant(n);
+    println!("常数阶的计算操作数量 = {}", count);
+
+    count = linear(n);
+    println!("线性阶的计算操作数量 = {}", count);
+    count = array_traversal(&vec![0; n as usize]);
+    println!("线性阶（遍历数组）的计算操作数量 = {}", count);
+
+    count = quadratic(n);
+    println!("平方阶的计算操作数量 = {}", count);
+
+    let mut nums = (1..=n).rev().collect::<Vec<_>>(); // [n,n-1,...,2,1]
+    count = bubble_sort(&mut nums);
+    println!("平方阶（冒泡排序）的计算操作数量 = {}", count);
+
+    count = exponential(n);
+    println!("指数阶（循环实现）的计算操作数量 = {}", count);
+    count = exp_recur(n);
+    println!("指数阶（递归实现）的计算操作数量 = {}", count);
+
+    count = logarithmic(n);
+    println!("对数阶（循环实现）的计算操作数量 = {}", count);
+    count = log_recur(n);
+    println!("对数阶（递归实现）的计算操作数量 = {}", count);
+
+    count = linear_log_recur(n.into());
+    println!("线性对数阶（递归实现）的计算操作数量 = {}", count);
+
+    count = factorial_recur(n);
+    println!("阶乘阶（递归实现）的计算操作数量 = {}", count);
+}
\ No newline at end of file