cf1073c 二分+二维前缀和

#include<bits/stdc++.h>
using namespace std;
#define maxn 200005
char s[maxn];
int tmp,n,x,y,sum[2][maxn];
map<char,int>mp;

int judge(int mid){//能否在mid长度内修改完 
    for(int l=1;l+mid-1<=n;l++){
        int r=l+mid-1;
        int Y=sum[0][n]-sum[0][r]+sum[0][l-1];
        int X=sum[1][n]-sum[1][r]+sum[1][l-1];
        int tot=abs(x-X)+abs(y-Y);//在区间[l,r]要走的距离 
        if(tot<=mid)return 1;
    }
    return 0;
}

int main(){
    mp['U']=1,mp['D']=-1,mp['L']=-1,mp['R']=1;
    cin>>n>>s+1>>x>>y;
    tmp=abs(x)+abs(y);
    if(n<tmp || tmp%2!=n%2){
        puts("-1");
        return 0;
    }
    
    for(int i=1;i<=n;i++){
        if(s[i]=='U'||s[i]=='D'){
            sum[0][i]=sum[0][i-1]+mp[s[i]];
            sum[1][i]=sum[1][i-1];
        }
        else {
            sum[0][i]=sum[0][i-1];
            sum[1][i]=sum[1][i-1]+mp[s[i]];
        }
    }
    
    int ans=-1,l=0,r=n,mid;
    while(l<=r){
        mid=l+r>>1;
        if(judge(mid))
            ans=mid,r=mid-1;
        else l=mid+1;
    }
    printf("%d
",ans);
}