LC LCP 20. 快速公交

link

class Solution {
public:
    #define LL long long 
    unordered_map<int,LL> memo;
    int busRapidTransit(int target, int inc, int dec, vector<int>& jump, vector<int>& cost) {
        int mod=1E9+7;
        return dfs(target,inc,dec,jump,cost)%mod;
    }

    LL dfs(int u, int inc, int dec, vector<int>& jump, vector<int>& cost){
        if(u==0) return 0;
        if(u==1) return inc;

        if(memo.find(u)!=memo.end()) return memo[u];
        LL res=(LL)inc*u;

        for(int i=0;i<jump.size();i++){
            if(u%jump[i]==0){
                res=min(res,(LL)cost[i]+dfs(u/jump[i],inc,dec,jump,cost));
            }else{
                if(u>jump[i]){
                    LL t=(LL)cost[i]+(LL)inc*(u%jump[i])+dfs(u/jump[i],inc,dec,jump,cost);
                    res=min(res,t);
                }
                LL t=(LL)cost[i]+(LL)dec*(jump[i]-u%jump[i])+dfs(u/jump[i]+1,inc,dec,jump,cost);
                res=min(res,t);
            }
        }

        return memo[u]= res;
    }
};