hdu 4046 Panda

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題意：即3個連續的wbw算是一個love，看一下某個區間共有多少個love，多次詢問。還有替換某個位置的字母，然後詢問。

用樹狀數組處理，題目並不難，但因為一處想當然錯了N次。。。

題目連結：

Panda

#include"stdio.h"#include"string.h"#define N 50005#define lowbit(i) (i&(-i))char str[N];int c[N],n;int judge(char c1,char c2,char c3){if(c1=='w'&&c2=='b'&&c3=='w')return 1;return 0;}void modify(int x,int d){int i;for(i=x;i<n;i+=lowbit(i))c[i]+=d;}int getsum(int x){int i,s=0;for(i=x;i>0;i-=lowbit(i))s+=c[i];return s;}void inti(){int i;for(i=2;i<n;i++){if(judge(str[i-2],str[i-1],str[i]))modify(i,1);}}int main(){int T,m,op,l,r,k,cnt=1;char ch;scanf("%d",&T);while(T--){scanf("%d%d",&n,&m);scanf("%s",str);memset(c,0,sizeof(c));inti();printf("Case %d:\n",cnt++);while(m--){scanf("%d",&op);if(op==0){scanf("%d%d",&l,&r);if(r-l<2){printf("0\n");continue;}printf("%d\n",getsum(r)-getsum(l+1));}else{scanf("%d %c",&k,&ch);if(str[k]==ch)continue;if(k>=2&&judge(str[k-2],str[k-1],str[k]))modify(k,-1);if(k>=2&&judge(str[k-2],str[k-1],ch))modify(k,1);if(k>=1&&k+1<n&&judge(str[k-1],str[k],str[k+1]))modify(k+1,-1);if(k>=1&&k+1<n&&judge(str[k-1],ch,str[k+1]))modify(k+1,1);if(k+2<n&&judge(str[k],str[k+1],str[k+2]))modify(k+2,-1);if(k+2<n&&judge(ch,str[k+1],str[k+2]))modify(k+2,1);str[k]=ch;}}}return 0;}