leetcode: Add index to 2574

src/SUMMARY.md

@@ -300,6 +300,8 @@
     - [2101-2200](leetcode/by-id/2101-2200.md)
         - [2108. 找出数组中的第一个回文字符串 Find First Palindromic String in the Array](leetcode/2108.find-first-palindromic-string-in-the-array/index.md)
         - [2119. 反转两次的数字 A Number After a Double Reversal](leetcode/2119.a-number-after-a-double-reversal/index.md)
+    - [2501-2600](leetcode/by-id/2501-2600.md)
+        - [2574. 左右元素和的差值 Left and Right Sum Differences](leetcode/2574.left-and-right-sum-differences/index.md)
     - [2801-2900](leetcode/by-id/2801-2900.md)
         - [2848. 与车相交的点 Points That Intersect With Cars](leetcode/2848.points-that-intersect-with-cars/index.md)
     - [3001-3100](leetcode/by-id/3001-3100.md)

src/leetcode/2574.left-and-right-sum-differences/Cargo.toml

@@ -1,5 +1,5 @@
 [package]
-name = "lc-0000-name"
+name = "lc-2574-left-and-right-sum-differences"
 version = "0.1.0"
 edition = "2021"
 publish = false

src/leetcode/2574.left-and-right-sum-differences/index.md

@@ -1,4 +1,19 @@
+# 2574. 左右元素和的差值 Left and Right Sum Differences
 
-# 
+[问题描述](https://leetcode.com/problems/left-and-right-sum-differences)
 
-[问题描述](https://leetcode.com/problems/)
+这是一个简单的前缀和 prefix sum 问题.
+
+## Prefix sum
+
+处理思路如下:
+
+1. 计算 `left_sum`, 从左到右遍历原数组, 并计算前缀和, `left_sum[i + 1] = left_sum[i] + nums[i]`
+2. 计算 `right_sum` 从左到右遍历原数组, 并计算前缀和, `right_sum[i - 1] = right_sum[i] + nums[i]`
+3. 计算遍历两个数组, 并计算 `(left_sum[i] - right_sum[i]).abs()`, 就得到了答案
+
+```rust
+{{#include src/main.rs:5:31}}
+```
+
+该算法的时间复杂度是 `O(n)`, 空间复杂度是 `O(n)`.

src/leetcode/2574.left-and-right-sum-differences/src/main.rs

@@ -9,21 +9,23 @@ pub fn left_right_difference1(nums: Vec<i32>) -> Vec<i32> {
     let len = nums.len();
     let mut left_sum = vec![0; len];
     left_sum[0] = 0;
+    // 从左向右遍历
     for i in 0..(len - 1) {
         left_sum[i + 1] = left_sum[i] + nums[i];
     }
     //println!("left sum: {left_sum:?}");
 
     let mut right_sum = vec![0; len];
     right_sum[0] = 0;
-    for i in 0..(len - 1) {
-        right_sum[i + 1] = right_sum[i] + nums[len - i - 1];
+    // 从右向左遍历
+    for i in (1..=(len - 1)).rev() {
+        right_sum[i - 1] = right_sum[i] + nums[i];
     }
     //println!("right sum: {right_sum:?}");
 
     left_sum
         .into_iter()
-        .zip(right_sum.into_iter().rev())
+        .zip(right_sum)
         .map(|(left, right)| (left - right).abs())
         .collect()
 }

src/leetcode/by-id/2501-2600.md

@@ -0,0 +1 @@
+# 2501-2600

src/leetcode/tags/prefix-sum.md

@@ -8,8 +8,9 @@
 4. [1480. 一维数组的动态和 Running Sum of 1d Array](../1480.running-sum-of-1d-array/index.md)
 5. [1732. 找到最高海拔 Find the Highest Altitude](../1732.find-the-highest-altitude/index.md)
 6. [1991. 找到数组的中间位置 Find the Middle Index in Array](../1991.find-the-middle-index-in-array/index.md)
-7. [2848. 与车相交的点 Points That Intersect With Cars](../2848.points-that-intersect-with-cars/index.md)
-8. [3028. 边界上的蚂蚁 Ant on the Boundary](../3028.ant-on-the-boundary/index.md)
+7. [2574. 左右元素和的差值 Left and Right Sum Differences](../2574.left-and-right-sum-differences/index.md)
+8. [2848. 与车相交的点 Points That Intersect With Cars](../2848.points-that-intersect-with-cars/index.md)
+9. [3028. 边界上的蚂蚁 Ant on the Boundary](../3028.ant-on-the-boundary/index.md)
 
 ## 中等