bzoj2120 数颜色

Posted 2020-08-11 MashiroSky

http://www.lydsy.com/JudgeOnline/problem.php?id=2120 (题目链接)

题意：给出一个n个数，m个询问，每次询问一个区间或修改一个数，求区间内不同的数有多少个。

solution 
　　分块。每次修改就暴力nlogn重新构块。 
　　对于分块的话，代码很好理解。

代码：

// bzoj2120
#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#include<cmath>
#include<vector>
#define MOD 1000000007
#define inf 2147483640
#define LL long long
#define free(a) freopen(a".in","r",stdin);freopen(a".out","w",stdout);
using namespace std;
inline LL getint() {
    LL x=0,f=1;char ch=getchar();
    while (ch>‘9‘ || ch<‘0‘) {if (ch==‘-‘) f=-1;ch=getchar();}
    while (ch>=‘0‘ && ch<=‘9‘) {x=x*10+ch-‘0‘;ch=getchar();}
    return x*f;
}

const int maxn=1000010;
int head[maxn],a[maxn],b[maxn],pre[maxn],pos[maxn],n,m,q,block;

void reset(int x) {
    int l=(x-1)*block+1,r=min(x*block,n);
    for (int i=l;i<=r;i++) pre[i]=b[i];
    sort(pre+l,pre+r+1);
}
void build() {
    for (int i=1;i<=n;i++) {
        b[i]=head[a[i]];
        head[a[i]]=i;
        pos[i]=(i-1)/block+1;
    }
    for (int i=1;i<=m;i++) reset(i);
}
int find(int x,int v) {
    int l=(x-1)*block+1,r=min(x*block,n);
    int f=l;
    while (l<=r) {
        int mid=(l+r)>>1;
        if (pre[mid]<v) l=mid+1;
        else r=mid-1;
    }
    return l-f;
}
int query(int l,int r) {
    int ans=0;
    if (pos[l]==pos[r]) {
        for (int i=l;i<=r;i++) if (b[i]<l) ans++;
    }
    else {
        for (int i=l;i<=block*pos[l];i++) if (b[i]<l) ans++;
        for (int i=block*(pos[r]-1)+1;i<=r;i++) if (b[i]<l) ans++;
    }
    for (int i=pos[l]+1;i<pos[r];i++) ans+=find(i,l);
    return ans;
}
void modify(int x,int y) {
    for (int i=1;i<=n;i++) head[a[i]]=0;
    a[x]=y;
    for (int i=1;i<=n;i++) {
        int t=b[i];
        b[i]=head[a[i]];
        if (t!=b[i]) reset(pos[i]);
        head[a[i]]=i;
    }
}
int main() {
    scanf("%d%d",&n,&q);
    for (int i=1;i<=n;i++) scanf("%d",&a[i]);
    block=int(sqrt(n));
    if (n%block>0) m=n/block+1;
    else m=n/block;
    build();
    while (q--) {
        char ch[10];
        int x,y;
        scanf("%s%d%d",ch,&x,&y);
        if (ch[0]==‘Q‘)
            printf("%d\n",query(x,y));
        else modify(x,y);
    }
    return 0;
}