Educational Codeforces Round 20 E. Roma and Poker

#include<bits/stdc++.h>

using namespace std;

#define X first
#define Y second
#define eps 1e-2
#define gcd __gcd
#define pb push_back
#define PI acos(-1.0)
#define lowbit(x) (x)&(-x)
#define bug printf("!!!!!\n");
#define mem(x,y) memset(x,y,sizeof(x))

typedef long long LL;
typedef long double LD;
typedef pair<int,int> pii;
typedef unsigned long long uLL;

const int maxn = 1e3+2;
const int INF  = 1<<30;
const int mod  = 1e9+7;
const int M=1e3+10;

int n,k,dp[maxn][M*2+10],pre[maxn][M*2+10];
char ch[maxn];
std::vector<char> res;
bool check(int pos){
    
    // cout<<pos<<endl;
    int fl=0;
    int now=n,pr=pre[now][pos];
    while(now){
    
        // cout<<pr<<" "<<pos<<endl;
        if(ch[now]=='?'){
    
            if(pr<pos) res.push_back('W');
            else if(pr>pos) res.push_back('L');
            else res.push_back('D');
        }else res.push_back(ch[now]);
        --now;pos=pr;pr=pre[now][pr];fl=1;
        // cout<<now<<endl;
    }
    return 1;
}
void solve(){
    
    scanf("%d%d",&n,&k);cin>>ch+1;
    dp[0][M]=1;
    for(int i=1;i<=n;i++){
    
        for(int j=1-k;j<=k-1;j++){
    
            if(dp[i-1][j+M]==0) continue;
            if(ch[i]=='L'||ch[i]=='?'){
    
                dp[i][j+M-1]=1;
                pre[i][j+M-1]=j+M;
            }
            if(ch[i]=='W'||ch[i]=='?'){
    
                dp[i][j+M+1]=1;
                pre[i][j+M+1]=j+M;
            }
            if(ch[i]=='D'||ch[i]=='?'){
    
                dp[i][j+M]=1;
                pre[i][j+M]=j+M;
            }
        }
    }
    // cout<<dp[n][M+k]<<" "<<dp[n][M-k]<<endl;
    if(dp[n][M+k]&&check(M+k)){
    for(int i=res.size()-1;i>=0;i--) cout<<res[i];cout<<endl;}
    else if(dp[n][M-k]&&check(M-k)){
    for(int i=res.size()-1;i>=0;i--) cout<<res[i];cout<<endl;}
    else{
    
        cout<<"NO"<<endl;
    }
    
    // if(==-1) {cout<<"NO"<<endl;return;}

    return;
}

int main()
{
    
// freopen("in.txt","r",stdin);
// freopen("out.txt","w",stdout);
// ios::sync_with_stdio(false);
    int t = 1;
    //scanf("%d",&t);
    while(t--){
    
    // printf("Case %d: ",cas++);
        solve();
    }
    return 0;
}