add: 最大交换

README.md

@@ -816,3 +816,7 @@ Rust标准库`std::collections`提供了4种通用容器类型，包含一下8
 - [统计整数数目](src/math/count_of_integers.rs)  [数学, 字符串, 动态规划]
 
   - LeetCode 2719. 统计整数数目 <https://leetcode.cn/problems/count-of-integers>
+
+- [最大交换](src/math/maximum_swap.rs)  [贪心, 数学]
+
+  - LeetCode 670. 最大交换 <https://leetcode.cn/problems/maximum-swap>

src/math/maximum_swap.rs

@@ -0,0 +1,31 @@
+// 最大交换
+// https://leetcode.cn/problems/maximum-swap
+// INLINE  ../../images/math/maximum_swap.jpeg
+
+pub struct Solution;
+
+impl Solution {
+    pub fn maximum_swap(num: i32) -> i32 {
+        let mut s: Vec<char> = num.to_string().chars().collect();
+        let n = s.len();
+        let mut max_idx = n - 1;
+        let mut idx1 = None;
+        let mut idx2 = None;
+
+        for i in (0..n).rev() {
+            if s[i] > s[max_idx] {
+                max_idx = i;
+            } else if s[i] < s[max_idx] {
+                idx1 = Some(i);
+                idx2 = Some(max_idx);
+            }
+        }
+
+        if let (Some(idx1), Some(idx2)) = (idx1, idx2) {
+            s.swap(idx1, idx2);
+            s.iter().collect::<String>().parse::<i32>().unwrap_or(num)
+        } else {
+            num
+        }
+    }
+}

src/math/mod.rs

@@ -21,3 +21,4 @@ pub mod maximum_students_taking_exam;
 pub mod day_of_the_week;
 pub mod maximum_rows_covered_by_columns;
 pub mod count_of_integers;
+pub mod maximum_swap;

tests/math/maximum_swap_test.rs

@@ -0,0 +1,20 @@
+use rust_practice::math::maximum_swap::Solution;
+
+#[test]
+fn maximum_swap_test() {
+    // 示例 1 :
+    // 输入: 2736
+    // 输出: 7236
+    // 解释: 交换数字2和数字7。
+    let num = 2736;
+    let result = Solution::maximum_swap(num);
+    assert_eq!(result, 7236);
+
+    // 示例 2 :
+    // 输入: 9973
+    // 输出: 9973
+    // 解释: 不需要交换。
+    let num = 9973;
+    let result = Solution::maximum_swap(num);
+    assert_eq!(result, 9973);
+}

tests/math/mod.rs

@@ -21,3 +21,4 @@ pub mod maximum_students_taking_exam_test;
 pub mod day_of_the_week_test;
 pub mod maximum_rows_covered_by_columns_test;
 pub mod count_of_integers_test;
+pub mod maximum_swap_test;