1+ class Solution {
2+ private:
3+ inline bool cmp1 (vector<int >::iterator a,
4+ vector<int >::iterator b)
5+ {
6+ if (*a >= 0 && *b >= 0 )
7+ {
8+ const unsigned ua = *a, ub = *b ;
9+ return ua <= (ub << 1 ) ;
10+ }
11+ 12+ if (*a < 0 && *b < 0 )
13+ {
14+ const unsigned ua = -*a, ub = -*b ;
15+ return ua >= (ub << 1 ) ;
16+ }
17+ 18+ if (*a < 0 && *b >= 0 )
19+ return true ;
20+ 21+ if (*a >= 0 && *b < 0 )
22+ return false ;
23+ }
24+ 25+ unsigned CountLRPairs (vector<int >::iterator start,
26+ vector<int >::iterator end)
27+ {
28+ if (start + 1 >= end)
29+ return 0 ;
30+ if (start + 2 == end)
31+ {
32+ if (*start <= *(start+1 ))
33+ return !cmp1 (start, start+1 ) ; // 这里也要计算,应为可能有负数
34+ else // 这边也要排序,需要特别注意排序的条件是a[i] < a[j],而逆序的条件是a[i] < 2*a[j]
35+ {
36+ swap (*start, *(start+1 )) ;
37+ return !cmp1 (start+1 , start) ; // 交换过位置了
38+ }
39+ }
40+ 41+ vector<int >::iterator mid = start + ((end-start) >> 1 ) ;
42+ vector<int >::iterator pF = start, pB = mid ;
43+ int cnt = CountLRPairs (start, mid) + CountLRPairs (mid, end) ;
44+ while (pF != mid)
45+ {
46+ while (pB != end && !cmp1 (pF, pB))
47+ ++pB ;
48+ cnt += pB-mid ;
49+ ++pF ;
50+ }
51+ 52+ vector<int > tmp (start, mid) ;
53+ pF = tmp.begin () ;
54+ pB = mid ;
55+ vector<int >::iterator p = start ;
56+ 57+ auto size = end - start ;
58+ if (size == 10 )
59+ ++size ;
60+ 61+ while (pF != tmp.end () && pB != end)
62+ {
63+ if (*pF <= *pB)
64+ *p++ = *pF++ ;
65+ else
66+ *p++ = *pB++ ;
67+ }
68+ while (pF != tmp.end ())
69+ *p++ = *pF++ ;
70+ while (pB != end)
71+ *p++ = *pB++ ;
72+ 73+ return cnt ;
74+ }
75+ public:
76+ int reversePairs (vector<int >& nums) {
77+ return CountLRPairs (nums.begin (), nums.end ()) ;
78+ }
79+ };
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