fix: solution

Author: yanglbme

solution/2200-2299/2218.Maximum Value of K Coins From Piles/README.md

@@ -208,7 +208,11 @@ function maxValueOfCoins(piles: number[][], k: number): number {
 
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-### 方法二
+### 方法二：动态规划（空间优化）
+
+我们可以发现，对于第 $i$ 组，我们只需要用到 $f[i - 1][j]$ 和 $f[i][j - h]$，因此我们可以将二维数组优化为一维数组。
+
+时间复杂度 $O(k \times L)$，空间复杂度 $O(k)$。
 
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solution/2200-2299/2218.Maximum Value of K Coins From Piles/README_EN.md

@@ -204,7 +204,11 @@ function maxValueOfCoins(piles: number[][], k: number): number {
 
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-### Solution 2
+### Solution 2: Dynamic Programming (Space Optimization)
+
+We can observe that for the $i$-th pile, we only need to use $f[i - 1][j]$ and $f[i][j - h]$, so we can optimize the two-dimensional array to a one-dimensional array.
+
+The time complexity is $O(k \times L)$, and the space complexity is $O(k)$.
 
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