leetcode: Add 0670

src/leetcode/0670.maximum-swap/Cargo.toml

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+[package]
+name = "lc-0670-maximum-swap"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]

src/leetcode/0670.maximum-swap/index.md

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+
+# 
+
+[问题描述](../problems/)

src/leetcode/0670.maximum-swap/src/main.rs

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+// Copyright (c) 2024 Xu Shaohua <[email protected]>. All rights reserved.
+// Use of this source is governed by General Public License that can be found
+// in the LICENSE file.
+
+use std::cmp::Ordering;
+
+// Greedy
+// 尽量将较大的位数往前放, 将较小的位数往后放.
+pub fn maximum_swap1(num: i32) -> i32 {
+    #[must_use]
+    fn from_digits(digits: &[i32]) -> i32 {
+        let mut num = 0;
+        for &digit in digits {
+            num = num * 10 + digit;
+        }
+        num
+    }
+
+    #[must_use]
+    fn to_digits(mut num: i32) -> Vec<i32> {
+        if num == 0 {
+            return vec![0];
+        }
+
+        let mut digits = Vec::new();
+        while num != 0 {
+            digits.push(num % 10);
+            num /= 10;
+        }
+        digits.reverse();
+        digits
+    }
+
+    debug_assert!(num >= 0);
+    // 先把整数转换成各个位数.
+    let mut digits: Vec<i32> = to_digits(num);
+    let mut left: usize = 0;
+
+    // 对整数位按照从大到小进行排序, 并记录其索引位置.
+    let mut sorted_digits: Vec<(usize, i32)> = digits.iter().copied().enumerate().collect();
+    sorted_digits.sort_unstable_by(|a: &(usize, i32), b: &(usize, i32)| match b.1.cmp(&a.1) {
+        Ordering::Equal => a.0.cmp(&b.0),
+        Ordering::Less => Ordering::Less,
+        Ordering::Greater => Ordering::Greater,
+    });
+    //println!("digits: {digits:?}, sorted: {sorted_digits:?}");
+
+    // 再从中找出最大的位数, 如果不是处于第一位, 就与第二位交换.
+    // 如果最大的位数是第一位, 就找出第二大的位数, 如果它不处于第二位, 就与第二位交换.
+    // 依次做下去, 直到遍历所有整数位.
+    while left < digits.len() {
+        if digits[left] != sorted_digits[left].1 {
+            // 考虑重复的位数, 如果有重复的位数, 就选索引值最高的那个.
+            let mut right = sorted_digits[left].0;
+            let mut i = left;
+            while i + 1 < digits.len() && sorted_digits[i].1 == sorted_digits[i + 1].1 {
+                right = sorted_digits[i + 1].0;
+                i += 1;
+            }
+            digits.swap(left, right);
+            break;
+        }
+        left += 1;
+    }
+
+    from_digits(&digits)
+}
+
+pub type SolutionFn = fn(i32) -> i32;
+
+fn check_maximum_swap(func: SolutionFn) {
+    assert_eq!(func(2736), 7236);
+    assert_eq!(func(9973), 9973);
+    assert_eq!(func(98368), 98863);
+    assert_eq!(func(1993), 9913);
+}
+
+fn main() {
+    check_maximum_swap(maximum_swap1);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{check_maximum_swap, maximum_swap1};
+
+    #[test]
+    fn test_maximum_swap1() {
+        check_maximum_swap(maximum_swap1);
+    }
+}