BOJ : https://www.acmicpc.net/
codeforce : codeforce.com
UVa : https://uva.onlinejudge.org/
SPOJ : http://www.spoj.com/
CSA : https://csacademy.com/
algospot : https://algospot.com/
HackerRank : HackerRank
SWEA : https://swexpertacademy.com/main/main.do
TopCoder : https://www.topcoder.com/
oj.uz : https://oj.uz/
AtCoder : https://beta.atcoder.jp/
programmers : https://programmers.co.kr/learn/challenges
GCJ : Code Jam
e-mail : [email protected]