题目 题意: 有n种化学物质,第i种物质现有bi千克,需要ai千克.有n-1种,编号为2-n的转换方式,每种都为(x,k),第i行是编号为i+1的转换方式,编号为i的转换方式(xi,ki)表示ki千克的xi物质可以转换成1千克的i物质,1千克的i物质可以转换成1千克的xi物质.问是否可能通过转换得到足够的需要的物质.(1 ≤ xj + 1 ≤ j) 重点:上面标红的条件.如果只保留ki千克的xi物质可以转换成1千克的i物质产生的一条有向边,表明xi物质连出的边一定是指向编号大于i的物质的(x[i…

There are n cities numbered from 1 to n in Berland. Some of them are connected by two-way roads. Each road has its own length — an integer number from 1 to 1000. It is known that from each city it is possible to get to any other city by existing road…

这题乍一看是一道水树形DP(其实事实上它确实是树形DP),然后设f[i]表示第i个点所多余/需要的材料,然后我们愉快的列出了式子: if(f[v]<0) f[u] += f[v] * edges[c_e].dis; else f[u] += f[v]; 然后放到CF上,直接WA,十分自闭,于是我试图define int long long,还是没过,仔细一想(偷瞄了一眼CF的数据),发现f数组有可能会爆long long,怎么办?高精? 显然这不太现实,于是想着如果它要爆了就把它置回边缘,实测不…

咸鱼选手发现自己很久不做cf了,晚节不保. A.Curriculum Vitae 枚举一下间断点的位置. #include<bits/stdc++.h> using namespace std; ; int cnt,n,a[N],mx,cur; inline int read(){ ,x=;char ch; ;}'); +ch-'); return f*x; } int main(){ n=read(); ;i<=n;i++)a[i]=read(); ; ;i<=n;i++){ c…

C. Amr and Chemistry Problem's Link: http://codeforces.com/problemset/problem/558/C Mean: 给出n个数,让你通过下面两种操作,把它们转换为同一个数.求最少的操作数. 1.ai = ai*2 2.ai = ai/2 (向下取整) analyse: 基本思路:首先枚举出每个数能够到达的数字并且记录下到达该数组需要的步数,然后从到达次数为n次的数字中选择步数最小的即为答案. 对于一个数字Ai,它可以变换得到的数字可…

B. Berland National LibraryTime Limit: 2 Sec Memory Limit: 256 MB 题目连接 http://codeforces.com/contest/567/problem/B Description Berland National Library has recently been built in the capital of Berland. In addition, in the library you can take any of…

DZY Loves Chemistry Time Limit:1000MS     Memory Limit:262144KB     64bit IO Format:%I64d & %I64u Submit Status Practice CodeForces 445B Description DZY loves chemistry, and he enjoys mixing chemicals. DZY has n chemicals, and m pairs of them will re…

B. Ancient Berland Hieroglyphs 题目连接: http://codeforces.com/problemset/problem/164/B Descriptionww.co Polycarpus enjoys studying Berland hieroglyphs. Once Polycarp got hold of two ancient Berland pictures, on each of which was drawn a circle of hierog…

C. Amr and Chemistry Time Limit: 20 Sec Memory Limit: 256 MB 题目连接 http://codeforces.com/contest/558/problem/C Description Amr loves Chemistry, and specially doing experiments. He is preparing for a new interesting experiment. Amr has n different type…

B. Berland National LibraryTime Limit: 20 Sec Memory Limit: 256 MB 题目连接 http://codeforces.com/contest/567/problem/B Description Berland National Library has recently been built in the capital of Berland. In addition, in the library you can take any o…