xiji333的博客

https://leetcode-cn.com/problems/minimum-cost-to-change-the-final-value-of-expression/ 思路：表达式问题做少了……看到给定的输入，显然是一个中缀表达式。如果显示建立出一棵对应的树，并用dp[i][j]dp[i][j]dp[i][j]表示把节点iii及其子树所代表的表达式的值修改为jjj所需要的最少操作次数，那么这就是一个树形dpdpdp问题。中缀表达式的性质在此不多赘述，假设已知两个节点a、ba、ba、b，那么当操作符号

https://vjudge.net/problem/HDU-1561 思路：稍微转化一下就是有依赖的背包问题了，当然也属于树形dpdpdp的范畴。这里就说一下怎么转化，认为每一个城堡的体积都是111，背包的总体积为mmm即可，当然有个细节要注意，就是点000的体积是000。 关于有依赖的背包问题，可以看我这篇博客的介绍： https://blog.youkuaiyun.com/xiji333/article...

http://acm.hdu.edu.cn/showproblem.php?pid=5909 题目大意：⼀棵NNN个节点的树，每个节点有⼀个权值viv_ivi​，⼦树的权值定义为子树内所有节点权值的异或和。问各个权值的子树分别有多少种？ 思路：设dp[u][i]dp[u][i]dp[u][i]表示以uuu为根的且权值为iii的子树的个数，初始时dp[i][a[i]]=1dp[i][a[i]]=...

http://codeforces.com/problemset/problem/1153/D Now Serval is a junior high school student in Japari Middle School, and he is still thrilled on math as before. As a talented boy in mathematics, he l...

http://acm.hdu.edu.cn/showproblem.php?pid=1520 There is going to be a party to celebrate the 80-th Anniversary of the Ural State University. The University has a hierarchical structure of employees. ...