http://www.geeksforgeeks.org/longest-repeating-and-non-overlapping-substring/

input="geeksforgeeks", output = "geeks"

local[i][j]代表以i和j结尾的字符串最长的重复长度,

• if s[i-1]==s[j-1] local[i][j] = local[i-1][j-1]+1

• else local[i][j]==0

• maxLen = max(maxLen, local[i][j]