add some oj source code
comment sjtu oj 1002 and standardize name
rewrite sjtu oj 1002 using prefix sum
delete sjtu oj 1001 for no value
rename sjtuoj_1003
rename sjtuoj_1003
Union data structure java implementation added
improve the solution of sjtu oj 1006
add the begin and end item number of the sequence
simple string add sjtu oj 1007
SJTUOJ binary tree construction and judgement
some oj added