The 36th ACM/ICPC Asia Regional Beijing Site&&http://acm.hdu.edu.cn/showproblem.php?pid=4046

比较难的线段树题，，，

#include<iostream>#include<cstdio>#include<string.h>#define N 50005using namespace std;typedef struct NODE{    int l;    int r;    int key;}Node;Node node[N<<2];char str[N];void build(int t,int l,int r){    node[t].l=l;    node[t].r=r;    if(r==l)    {        if(l<=2) {node[t].key=0;return;}        if(str[l]=='w'&&str[l-1]=='b'&&str[l-2]=='w') node[t].key=1;        else  node[t].key=0;        return;    }    int mid=(l+r)>>1;    build(t<<1,l,mid);    build(t<<1|1,mid+1,r);    node[t].key=node[t<<1].key+node[t<<1|1].key;}void update(int t,int l,int r,char ch){    if(node[t].l==l&&node[t].r==r)    {         str[l]=ch;        if(l<=2) return;        if(str[l]=='w'&&str[l-1]=='b'&&str[l-2]=='w') node[t].key=1;        else  node[t].key=0;        return ;    }    if(l>=node[t<<1|1].l)  update(t<<1|1,l,r,ch);    else if(r<=node[t<<1].r) update(t<<1,l,r,ch);    else    { update(t<<1,l,node[t<<1].r,ch);      update(t<<1|1,node[t<<1|1].l,r,ch);    }    node[t].key=node[t<<1].key+node[t<<1|1].key;}int Quary(int t,int l,int r){    if(node[t].l==l&&node[t].r==r) return node[t].key;    if(l>=node[t<<1|1].l) return Quary(t<<1|1,l,r);    else if(r<=node[t<<1].r) return Quary(t<<1,l,r);    else  return Quary(t<<1,l,node[t<<1].r)+Quary(t<<1|1,node[t<<1|1].l,r);}int main(){    int T;    scanf("%d",&T);    for(int k=1;k<=T;++k)     {         printf("Case %d:\n",k);         int n,m;        scanf("%d%d",&n,&m);         str[0]=0;         scanf("%s",str+1);         build(1,1,n);         for(int i=0;i!=m;++i)         {             int x;             scanf("%d",&x);             if(x==0)                   {  int y,z;                   scanf("%d%d",&y,&z);                     if(z-y+1<3) printf("0\n");                     else  printf("%d\n",Quary(1,y+3,z+1));                 }             else             {                 int y;                 char z;                scanf("%d",&y);getchar();scanf("%c",&z);                 update(1,y+1,y+1,z);                 if(y+1<n) update(1,y+2,y+2,str[y+2]);                 if(y+2<n) update(1,y+3,y+3,str[y+3]);            }         }     }return 0;}