树状数组笔记
代码越短，理解越难~
树状数组维护序列
1 #include<algorithm>
2 #include<iostream>
3 #include<cstring>
4 #include<cstdio>
5 #include<cmath>
6 #define lowbit(a) (a&-a)
7 using namespace std;
8 int n,q,l,r,a[100001],tree[400001];
9 char ord[5];
10 void add(int u,int val){
11 for(;u<=n;u+=lowbit(u)){
12 tree[u]+=val;
13 }
14 }
15 int query(int u){
16 int ans=0;
17 for(;u>0;u-=lowbit(u)){
18 ans+=tree[u];
19 }
20 return ans;
21 }
22 int main(){
23 memset(tree,0,sizeof(tree));
24 scanf("%d%d",&n,&q);
25 for(int i=1;i<=n;i++){
26 scanf("%d",&a[i]);
27 add(i,a[i]);
28 }
29 for(int i=1;i<=q;i++){
30 scanf("%s%d%d",ord,&l,&r);
31 if(ord[0]=='A'){
32 add(l,r);
33 }else if(ord[0]=='Q'){
34 printf("%d\n",query(r)-query(l-1));
35 }
36 }
37 return 0;
38 }
逆序数对
（为什么反而更短？？？）
1 #include<algorithm>
2 #include<iostream>
3 #include<cstring>
4 #include<cstdio>
5 #include<cmath>
6 #define lowbit(n) (n&-n)
7 typedef long long ll;
8 using namespace std;
9 int n,s,ans=0,tree[400001];
10 void add(int u,int val){
11 for(;u<=n;u+=lowbit(u)){
12 tree[u]+=val;
13 }
14 }
15 int query(int u){
16 int ans=0;
17 for(;u>0;u-=lowbit(u)){
18 ans+=tree[u];
19 }
20 return ans;
21 }
22 int main(){
23 scanf("%d",&n);
24 for(int i=1;i<=n;i++){
25 scanf("%d",&s);
26 ans+=(i-1-query(s-1));
27 add(s,1);
28 }
29 printf("%d",ans);
30 return 0;
31 }
