洛谷 P2658 汽车拉力比赛

题目传送门

解题思路:

二分答案,然后bfs验证,如果从一个路标可以达到其它所有路标,则答案可行.知道找到最佳答案.

AC代码:

 #include<iostream>
 #include<cstdio>
 #include<cmath>
 #include<cstring>
 #include<queue>

 using namespace std;

 int m,n,a[][],l,r,num,sum,ans,mid;
 int dx[] = {-,,,},dy[] = {,,,-};
 bool vis[][],v[][],flag,pp;

 inline bool check(int len,int x,int y) {
     queue<int> q,q1;
     q.push(x);
     q1.push(y);
     v[x][y] = ;
     while(!q.empty()) {
         x = q.front();
         y = q1.front();
         q.pop();
         q1.pop();
         if(vis[x][y] == ) num++;
         if(num == sum) return true;
         for(int i = ;i < ; i++) {
             int xx = x + dx[i];
             int yy = y + dy[i];
             if(abs(a[xx][yy] - a[x][y]) > len) continue;
             if(xx <  || xx > m || yy <  || yy > n) continue;
             if(!v[xx][yy]) {
                 q.push(xx);
                 q1.push(yy);
                 v[xx][yy] = ;
             }
         }
     }
     return false;
 }

 int main() {
     int x,y;
     scanf("%d%d",&m,&n);
     for(int i = ;i <= m; i++)
         for(int j = ;j <= n; j++){
             scanf("%d",&a[i][j]);
             r = max(r,a[i][j]);
         }
     for(int i = ;i <= m; i++)
         for(int j = ;j <= n; j++) {
             int u;
             scanf("%d",&u);
             if(u == )
                 vis[i][j] = ,sum++,x = i,y = j;
         }
     while(l < r) {
         mid = (l + r) / ;
         memset(v,,sizeof(v));
         flag = false;
         num = ;
         if(check(mid,x,y))
             r = mid,ans = mid;
         else
             l = mid + ;
     }
     printf("%d",ans);
     return ;
 }