【leetcode最短路】818. Race Car

https://leetcode.com/problems/race-car/description/

1. BFS剪枝 0<=current position<=2*target。为什么2*target有点不太明白

 class Solution {
 public:
     int dp[];
     struct Node{
         int pos;
         int speed;
         int step;
         Node(int p,int s,int ss){
             pos=p;
             speed=s;
             step=ss;
         }
     };
     int racecar(int target) {
         queue<Node> Q;
         set<pair<int,int> > vis;
         Q.push(Node(,,));
         vis.insert({,});
         while(!Q.empty()){
             Node q=Q.front();
             Q.pop();
             if(q.pos==target) return q.step;
             if(vis.find({q.pos+q.speed,q.speed*})==vis.end()&&q.pos+q.speed>=&&q.pos+q.speed<=*target){
                 vis.insert({q.pos+q.speed,q.speed*});
                 Q.push(Node(q.pos+q.speed,q.speed*,q.step+));
             }
             if(vis.find({q.pos,q.speed>?-:})==vis.end()){
                 vis.insert({q.pos,q.speed>?-:});
                 Q.push(Node(q.pos,q.speed>?-:,q.step+));
             }
         }
         return -;
     }
 };

2. Dijkstra，官方题解，没太看懂

3. DP

 class Solution {
 public:
     int dp[];
     int racecar(int target) {
         if(dp[target]!=) return dp[target];
         int bound;
         for(int i=;i<;i++){
             if((<<i)-==target) return dp[target]=i;
             if((<<i)->target){
                 bound=i;
                 break;
             }
         }
         dp[target]=bound++racecar((<<bound)--target);
         for(int i=;i<bound-;i++){
             dp[target]=min(dp[target],bound-++i++racecar(target-(((<<(bound-))-)-((<<i)-))));
         }
         return dp[target];
     }
 };