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uva 12086

树状数组

1. 求区间和

2. 单点赋值

还是单点改，通过维护一个a[ i ]，来求改变值

  #include <iostream>
  #include <cstring>
  #include <sstream>
  using namespace std;
   const int  N=2e5+4;
  int n,a[N],c[N];
   
   int lowbit(int x){ return x&-x; }
 void set(int x,int v){
    int d=v-a[x];
    a[x]+=d;
    for(;x<=n;x+=lowbit(x)) c[x]+=d;
 }
 int qq(int x){
    int r=0;
    for(;x;x-=lowbit(x)) r+=c[x];
    return r;
 }
   
 int main(){
    int j=0;
    bool k=0;
    while(cin>>n){
        j++;
        memset(a,0,sizeof(a));
        memset(c,0,sizeof(c));
        if(n==0)return 0;
        if(k)cout<<'\n';
        k=1;
        cout<<"Case "<<j<<':'<<'\n';
        for(int i=1;i<=n;i++){
            int x;
            cin>>x;
            set(i,x);
        }
        string s;
        getline(cin,s);
        while(getline(cin,s)){
            stringstream ss(s);
            char str;
            int x,y;
            if(s=="END")break;
            else if(s[0]=='M'){ 
                ss>>str>>x>>y;
                cout<<qq(y)-qq(x-1)<<'\n';
            }else if(s[0]=='S'){
                ss>>str>>x>>y;
                set(x,y);
            }
        }
    }
} 