WA in SPOJ Histogram problem

#	User	Rating
1	tourist	3985
2	jiangly	3814
3	jqdai0815	3682
4	Benq	3529
5	orzdevinwang	3526
6	ksun48	3517
7	Radewoosh	3410
8	hos.lyric	3399
9	ecnerwala	3392
9	Um_nik	3392

#	User	Contrib.
1	cry	169
2	maomao90	162
2	Um_nik	162
4	atcoder_official	160
5	djm03178	158
6	-is-this-fft-	157
7	adamant	155
8	Dominater069	154
8	awoo	154
10	luogu_official	150

Solving HISTOGRA problem on Spoj. Getting WA with this O(ln(N)*N) union-find-based solution. Can't find the bug myself, maybe somebody's fresh eyes can help. Much appreciated.

aalexand's blog