1 #include<bits/stdc++.h>  2   3 #define N 2222  4 using namespace std;  5 typedef long long ll;  6 #define inf 0x3f3f3f  7 int n;  8 int f[N],vis[N];  9 int a[N][N]; 10  11 struct node 12 { 13     int u,v,w; 14     node(int uu,int vv,int ww):u(uu),v(vv),w(ww){} 15 }; 16  17 vector<pair<int,int> > G[N]; 18 vector<node> edge; 19  20 int find(int x) 21 {if (f[x]!=x) return f[x]=find(f[x]);} 22  23 int cmp(node a,node b){return a.w<b.w;} 24  25 ll dis[N]; 26 void dfs(int x) 27 { 28    vis[x]=1; 29  //  cout<<dis[x]<<" "; 30    for (int i=0;i<G[x].size();i++) 31    { 32        int v=G[x][i].first; 33        int w=G[x][i].second; 34        if (vis[v]) continue; 35        dis[v]=dis[x]+w; 36        dfs(v); 37    } 38 } 39  40 int solve() 41 { 42     for (int i=1;i<n;i++) 43     for (int j=i+1;j<=n;j++) 44          edge.push_back(node(i,j,a[i][j])); 45  46     for (int i=1;i<=n;i++) f[i]=i; 47  48     sort(edge.begin(),edge.end(),cmp); 49     int t=edge.size(); 50     for (int i=0;i<t;i++) 51     { 52         int x=edge[i].u; 53         int y=edge[i].v; 54         int tx=find(x); 55         int ty=find(y); 56         if (tx!=ty) 57         { 58             f[tx]=ty; 59             G[x].push_back(make_pair(y,edge[i].w)); 60             G[y].push_back(make_pair(x,edge[i].w)); 61         } 62     } 63  64  65     for (int i=1;i<=n;i++) 66     { 67         memset(vis,0,sizeof(vis)); 68         memset(dis,0,sizeof(dis)); 69         dfs(i); 70  71         for (int j=1;j<=n;j++) 72         if (dis[j]!=a[i][j]) 73         { 74             return 0; 75         } 76     } 77     return 1; 78 } 79  80 int main() 81 { 82  83    scanf("%d",&n); 84     for (int i=1;i<=n;i++) 85     for (int j=1;j<=n;j++) 86       scanf("%d",&a[i][j]); 87  88     for (int i=1;i<=n;i++) 89     for (int j=1;j<=n;j++) 90     { 91        if (a[i][j]!=a[j][i]||i==j&&a[i][j]!=0) 92        { 93            puts("NO"); 94            return 0; 95        } 96        if (i!=j&&a[i][j]==0) 97            { 98             puts("NO"); 99            return 0;100            }101     }102 103  if (solve())  puts("YES");104  else  puts("NO");105  return 0;106 }

 1 #include<bits/stdc++.h> 2 typedef long long ll; 3 using namespace std; 4 #define N 2222 5  6  7 int a[N][N]; 8 int n; 9 int main()10 {11     scanf("%d",&n);12     for (int i=1;i<=n;i++)13     for (int j=1;j<=n;j++)14     scanf("%d",&a[i][j]);15     16     //预处理判断17     int flag=0;18     for (int i=1;i<=n;i++)19     for (int j=1;j<=n;j++)20     {21        if (i!=j&&a[i][j]==0) flag=1;22        if (i==j&&a[i][j]!=0)   flag=1;23        if (i!=j&&a[i][j]!=a[j][i]) flag=1;24        }25        26        if (flag)27        {28            puts("NO");29            return 0;30         }31 32     for (int i=1;i<=n;i++)33     {34         int inf= 1900000000;//初始的值要比较大些35         int pos=-1;36         for (int j=1;j<=n;j++){37         if (i==j) continue;38         if (a[i][j]<inf)39         {40             inf =a[i][j];41             pos=j;42             }43         }44         for (int j=1;j<=n;j++)45         {46             if (i==j||j==pos) continue;47             if (abs(a[i][j]-a[pos][j])!=inf)48             {49                 puts("NO");50                 return 0;51             }52         }53     }54 55    puts("YES");56    return 0;57 }

后面的基本是水体了：
C：贪心：
从第一的判断每次找合理值，矛盾就错误！
B:
我是用贪心的做法！
想想我们最后电梯还是要回到第一层！对吧！
也要走到最高层，当前有人想去的最高层！
那么我们每次把前K高层的先送上去！就能满足答案最小！

 1 #define N 111111 2 using namespace std; 3  4  5 int a[2222]; 6 int cmp(int x,int y) 7 { 8     return x>y; 9 }10 int main()11 {12     int n,k;13     cin>>n>>k;14     15     for (int i=1;i<=n;i++) cin>>a[i];16     sort(a+1,a+n+1,cmp);17     int ans=0;18     for (int i=1;i<=n;i+=k)19         ans+=(a[i]-1)*2;20 21     cout<<ans<<endl;22     return 0;

 复杂度O(N^2);时间600MS;这是快