POJ 1321 棋盘问题 (DFS + 回溯)
传送门：棋盘问题
人一我百！人十我万！永不放弃～～～怀着自信的心，去追逐梦想 ——kuangbin
Problem
Description
在一个给定形状的棋盘（形状可能是不规则的）上面摆放棋子，棋子没有区别。要求摆放时任意的两个棋子不能放在棋盘中的同一行或者同一列，请编程求解对于给定形状和大小的棋盘，摆放 k 个棋子的所有可行的摆放方案 C。
2018 牛客网暑期 ACM 多校训练营（第五场）A gpa 01 分数规划
传送门： 2018 牛客网暑期 ACM 多样训练营（第五场）A gpa
Description
题目描述
At the university where she attended, the final score of her is ${\sum{s[i]c[i]} \over \sum{s[i]}}$
Now she can delete at most k courses and she want to know what the highest final score that can get.
CodeForces 471D MUH and Cube Walls (KMP + 差分)
D. MUH and Cube Walls
time limit per test: 2 seconds
memory limit per test: 256 megabytes
input: standard input
output: standard output
memory limit per test: 256 megabytes
input: standard input
output: standard output
Description
Polar bears Menshykov and Uslada from the zoo of St. Petersburg and elephant Horace from the zoo of Kiev got hold of lots of wooden cubes somewhere. They started making cube towers by placing the cubes one on top of the other. They defined multiple towers standing in a line as a wall. A wall can consist of towers of different heights.
CodeForces 825F String Compression (KMP 求循环节 + DP)
F. String Compression
time limit per test: 2 seconds
memory limit per test: 512 megabytes
input: standard input
output: standard output
memory limit per test: 512 megabytes
input: standard input
output: standard output
Description
Ivan wants to write a letter to his friend. The letter is a string s consisting of lowercase Latin letters.
Unfortunately, when Ivan started writing the letter, he realised that it is very long and writing the whole letter may take extremely long time. So he wants to write the compressed version of string s instead of the string itself.
CodeForces 731C Socks (并查集)
C. Socks
time limit per test: 2 seconds
memory limit per test: 256 megabytes
input: standard input
output: standard output
memory limit per test: 256 megabytes
input: standard input
output: standard output
Description
Arseniy is already grown-up and independent. His mother decided to leave him alone for m days and left on a vacation. She have prepared a lot of food, left some money and washed all Arseniy’s clothes.
CodeForces 911D Inversion Counting (思维)
D. Inversion Counting
time limit per test: 2 seconds
memory limit per test: 256 megabytes
input: standard input
output: standard output
memory limit per test: 256 megabytes
input: standard input
output: standard output
Description
A permutation of size n is an array of size n such that each integer from 1 to n occurs exactly once in this array. An inversion in a permutation p is a pair of indices (i, j) such that i > j and a**i < *a**j*. For example, a permutation [4, 1, 3, 2] contains 4 inversions: (2, 1), (3, 1), (4, 1), (4, 3).
CodeForces 920F SUM and REPLACE (线段树)
F. SUM and REPLACE
time limit per test: 2 seconds
memory limit per test: 256 megabytes
input: standard input
output: standard output
memory limit per test: 256 megabytes
input: standard input
output: standard output
Description
Let D(x) be the number of positive divisors of a positive integer x. For example, D(2) = 2 (2 is divisible by 1 and 2), D(6) = 4 (6 is divisible by 1, 2, 3 and 6).
CodeForces 703D Mishka and Interesting sum (树状数组)
D. Mishka and Interesting sum
time limit per test: 3.5 seconds
memory limit per test: 256 megabytes
input: standard input
output: standard output
memory limit per test: 256 megabytes
input: standard input
output: standard output
Description
Little Mishka enjoys programming. Since her birthday has just passed, her friends decided to present her with array of non-negative integers a1, a2, …, an of n elements!
判断语句中位运算符的一个小坑
最近训练时敲代码总爱在 if 语句中有位算符时踩坑， 比如 if(i&1==0) 或 if(i&i-1 == 0)，本意是想判 i 是否为偶数和 i 是否为 2 的幂，但这么写都是错误的，导致程序不能输出正确结果。每次 debug 时又不明所以，耗了很长时间才找到。在这里记录下。
错误的原因是 == 运算符优先级要高于 & | ^ 这三个位运算符，故导致上面代码的判断顺序实际为 if(i & (1==0)) 和 if(i & (i-1 == 0))。 很痛苦呀，有没有。
建议：
- 判断式中如果同时存在位运算符和小于等于大于时，将位运算符表达式加上括号
- 判等时，如果一边是常数一边是变量，将常数放于判等左边。 （TAT，当时听郝斌老师讲这条时还不以为意，心想判等自己肯定不会写成 = , 现在想来，真是内牛满面呀，这条规则实在太好了）