【线段树延迟更新】HDU 3275

以后再补解题报告，先贴代码http://acm.hdu.edu.cn/showproblem.php?pid=3275

#define N 100005
char str[N];
int sum0[N*4],sum1[N*4];
bool mark[N*4];
void up(int id){
    sum0[id] = sum0[id<<1] + sum0[id<<1|1];
    sum1[id] = sum1[id<<1] + sum1[id<<1|1];
}
void build(int s,int t,int id){
    mark[id] = 0;
    if(s == t){
        if(str[s] == '0'){
            sum0[id] = 1;
            sum1[id] = 0;
        } else {
            sum0[id] = 0;
            sum1[id] = 1;
        }
        return ;
    }
    int mid = (s+t)>>1;
    build(s,mid,id<<1);
    build(mid+1,t,id<<1|1);
    up(id);
}
void rev(int id){
    mark[id] = !mark[id];
    swap(sum0[id],sum1[id]);
}
void down(int id){
    if(mark[id]){
        mark[id] = 0;
        rev(id<<1);
        rev(id<<1|1);
    }
}
void solve(int s,int t,int id,int l,int r){
    if(s<=l && r<=t){
        rev(id);
        return ;
    }
    down(id);
    int mid = (l+r)>>1;
    if(s<=mid)solve(s,t,id<<1,l,mid);
    if(mid+1<=t)solve(s,t,id<<1|1,mid+1,r);
    up(id);
}
int find(int s,int t,int id){
    if(s == t){
        if(sum0[id]>0)return s;
    }
    down(id);
    int mid = (s+t)>>1;
    if(sum0[id<<1])return find(s,mid,id<<1);
    else if(sum0[id<<1|1])return find(mid+1,t,id<<1|1);
    else return 0;
}
int main(){
    int n,k;
    while(scanf("%d%d",&n,&k) && (n+k)){
        int i,j;
        scanf("%s",str+1);
        bool ok = 1;
        int len = strlen(str+1);
        for(i=1;i<=len;i++){
            if(str[i] == '0'){
                ok = 0;
                break;
            }
        }
        if(ok){
            printf("0\n");
            continue;
        }
        if(k == 0){
            if(ok)printf("0\n");
            else printf("-1\n");
        } else {
            build(1,n,1);
            int ans = 0;
            while(1){
                int pos = find(1,n,1);//cout<<pos<<"!"<<endl;
                if(pos == 0){
                    ok = 1;
                    break;
                }
                if(ans>n-k+1 || pos+k-1>n){
                    ok = 0;
                    break;
                }
                solve(pos,pos+k-1,1,1,n);
                ans++;
            }
            if(!ok){
                printf("-1\n");
            } else {
                printf("%d\n",ans);
            }
        }
    }
    return 0;
}