沒有網址qwq

沒有oj

翻樹狀陣列看到求逆序對先複習一下歸併求逆序對qwq

逆序對真是個神奇的東西啊QAQ

純屬隨手一打隨手一貼quq

 1 #include<cstdio>
 2 #include<iostream>
 3 using namespace std;
 4 int n, a[100010], b[100010], cnt = 0;
 5 void merge_sort(int l, int r) {
 6     if(r-l > 0) {
 7         int mid = (l+r)/2;
 8         int i = l, p = l, q = mid+1
 
;
 9         merge_sort(l, mid);
10         merge_sort(mid+1, r);
11         while(p <= mid || q <= r) {
12             if(q > r || ((p<=mid) && a[p] <= a[q])) //p<=mid !!!!!別打成p<mid！！！ 
13                 b[i++] = a[p++];
14             else b[i++] = a[q++], cnt = cnt + (mid - p  + 1
 
);
15             //mid - 當前已經比較到哪個元素了 （p）
16             //別減成i 或者 l  
17         }
18         for(int i = l; i <= r; i++)
19             a[i] = b[i];
20     }
21 }
22 int main() {
23     scanf("%d", &n);
24     for(int i = 1; i <= n; i++) {
25         scanf("%d", &a[i]);
26     }
 
27     merge_sort(1, n);
28     printf("qwq排序後：\n");
29     for(int i = 1; i <= n; i++) 
30         cout<<a[i]<<' ';
31     cout<<endl<<"quq逆序對數："<<cnt<<endl;
32     return 0;
33 }