CodeForces413E Maze 2D

Posted 2021-01-10 yicongli

题意

给一个(2*n)的迷宫，有障碍物，(m)次询问，每次查询两点间最短路

题解

把上下当成一个点，每个点有上下两个接口
用线段树维护即可

#include<bits/stdc++.h>

using namespace std;

#define gc c=getchar()
#define r(x) read(x)
#define ls (rt<<1)
#define rs (rt<<1|1)

template<typename T>
inline void read(T&x){
    x=0;T k=1;char gc;
    while(!isdigit(c)){if(c==‘-‘)k=-1;gc;}
    while(isdigit(c)){x=x*10+c-‘0‘;gc;}x*=k;
}

const int INF=1e9;

const int N=2e5;

char s[2][N];

struct seg{
    int dist[2][2];
    
    const int* operator [](const int &x)const{
        return dist[x];
    }
    
    int* operator [](const int &x){
        return dist[x];
    }
    
}tr[N<<2];

inline seg operator +(const seg &a,const seg &b){
    seg ret;
    int ans;
    ans=INF;
    ans=min(ans,a[0][0]+b[0][0]+1);
    ans=min(ans,a[0][1]+b[1][0]+1);
    ret[0][0]=ans;
    ans=INF;
    ans=min(ans,a[0][0]+b[0][1]+1);
    ans=min(ans,a[0][1]+b[1][1]+1);
    ret[0][1]=ans;
    ans=INF;
    ans=min(ans,a[1][0]+b[0][1]+1);
    ans=min(ans,a[1][1]+b[1][1]+1);
    ret[1][1]=ans;
    ans=INF;
    ans=min(ans,a[1][0]+b[0][0]+1);
    ans=min(ans,a[1][1]+b[1][0]+1);
    ret[1][0]=ans;
    return ret;
}

inline void build(int rt,int l,int r){
    if(l==r){
        tr[rt][0][0]=tr[rt][0][1]=tr[rt][1][1]=tr[rt][1][0]=INF;
        if(s[0][l]==‘.‘){
            tr[rt][0][0]=0;
            if(s[1][l]==‘.‘)tr[rt][0][1]=1;
        }
        if(s[1][l]==‘.‘){
            tr[rt][1][1]=0;
            if(s[0][l]==‘.‘)tr[rt][1][0]=1;
        }
        return;
    }
    int mid=(l+r)>>1;
    build(ls,l,mid);
    build(rs,mid+1,r);
    tr[rt]=tr[ls]+tr[rs];
}

inline seg query(int rt,int l,int r,int x,int y){
    if(x<=l&&r<=y)return tr[rt];
    int mid=(l+r)>>1;
    if(y<=mid)return query(ls,l,mid,x,y);
    else if(x>mid)return query(rs,mid+1,r,x,y);
    else return query(ls,l,mid,x,y)+query(rs,mid+1,r,x,y);
}

int n,m;

inline int Query(int x,int y){
    int l=(x-1)%n+1;
    int r=(y-1)%n+1;
    if(l>r)swap(l,r),swap(x,y);
    return query(1,1,n,l,r)[x>n][y>n];
}

int main(){
    r(n),r(m);
    scanf("%s",s[0]+1);
    scanf("%s",s[1]+1);
    build(1,1,n);
    for(int a,b;m;--m){
        r(a),r(b);
        int ans=Query(a,b);
        if(ans==INF)ans=-1;
        printf("%d
",ans);
    }
}