列出一些用于算法题目学习与训练的网站：
UVA Online Judge： https://onlinejudge.org/
Sphere Online Judge: https://www.spoj.com/
Coderbyte: https://www.coderbyte.com/
Project Euler: http://projecteuler.com/
HackerRank: https://www.hackerrank.com/
CodeChef: https://www.codechef.com/
Top Coder: https://www.topcoder.com/
freeCodeCamp: https://www.freecodecamp.cn/
leetcode:https://leetcode-cn.com/