[arts] 2027.07.26

content/arts/2024/07.28.md

@@ -0,0 +1,67 @@
++++
+title = "ARTS 2024.07.26"
+date = 2024-07-28
+
+[taxonomies]
+tags = ["ARTS"]
++++
+
+## Algorithm
+
+[2865. 美丽塔 I - 力扣（LeetCode）](https://leetcode.cn/problems/beautiful-towers-i/description/)
+
+单调栈。从前往后，记录当前高度下，左边允许的最大的高度和。注意，如果当前高度大于前一个，可以则高度和增加，如果当前高度小于前边，找到第一个小于自己的下标k，高度和为 headSum[k] + (i - k) * h，i为当前坐标。这是一个单调栈
+
+```java
+class Solution {
+    public long maximumSumOfHeights(int[] heights) {
+        // height, index, sum
+        Deque<long[]> stk = new ArrayDeque<>();
+        stk.addFirst(new long[]{0, -1, 0});
+        long[] sums = new long[heights.length];
+        int len = heights.length;
+        for (int i = 0; i < len; i++) {
+            long h = heights[i];
+            while (h <= stk.peekFirst()[0]) {
+                stk.removeFirst();
+            }
+            long[] peek = stk.peekFirst();
+            long sum = peek[2] + h * (i - peek[1]);
+            sums[i] = sum;
+            stk.addFirst(new long[]{h, i, sum});
+        }
+
+        stk.clear();
+        stk.addFirst(new long[]{0, len, 0});
+        long ret = 0;
+        for (int i = len - 1; i >= 0; i--) {
+            long h = heights[i];
+            while (h <= stk.peekFirst()[0]) {
+                stk.removeFirst();
+            }
+            long[] peek = stk.peekFirst();
+            long sum = peek[2] + h * (peek[1] - i);
+            stk.addFirst(new long[]{h, i, sum});
+            ret = Math.max(ret, sum + sums[i] - h);
+        }
+        return ret;
+    }
+}
+```
+
+## Review
+
+- <https://news.ycombinator.com/item?id=41060102>
+- <https://trufflesecurity.com/blog/anyone-can-access-deleted-and-private-repo-data-github>
+
+Github fork 网络的底层机制，导致用户删除commit、删除repo、private fork的行为与普通用户的认知不一致，删除的数据仍然可以通过存在的fork访问到。
+
+Github了解这个问题，并且在文档中做了说明，但问题仍然是问题
+
+## Tips
+
+## Share
+
+[基本功 | 一文讲清多线程和多线程同步 (qq.com)](https://mp.weixin.qq.com/s?__biz=MjM5NjQ5MTI5OA==&mid=2651778446&idx=1&sn=44306b644777a4d939730e7774071541)
+
+多线程和多线程同步介绍的一篇文章，篇幅很长，涉及到一些cpu底层细节，值得一看