HDU 4034 graph (Floyd)

Given the shortest path between the source image vertices, the source image has at least several edges.

Analysis: if the distance between two points can be replaced by the other two sides, you can delete the edge. If there is a path shorter than the distance between the two points, "impossible ".

View code

 1 /* 2 Author:Zhaofa Fang 3 Lang:C++ 4 */ 5 #include <cstdio> 6 #include <cstdlib> 7 #include <iostream> 8 #include <cmath> 9 #include <cstring>10 #include <algorithm>11 #include <string>12 #include <utility>13 #include <vector>14 #include <queue>15 #include <stack>16 #include <map>17 #include <set>18 using namespace std;19 typedef long long ll;20 #define pii pair<int,int>21 #define pb push_back22 #define mp make_pair23 #define fi first24 #define se second25 #define lowbit(x) (x&(-x))26 const int INF = 2147483647;27 28 int maz[105][105];29 int floyd(int n)30 {31     int cnt = 0;32     for(int k=0;k<n;k++)33     {34         for(int i=0;i<n;i++)35         {36             for(int j=0;j<n;j++)37             {38                 if(i == k || j == k || i == k)continue;39                 if(maz[i][k] == -1 || maz[k][j] == -1 || maz[i][j] == -1)continue;40                 if(maz[i][j] > maz[i][k] + maz[k][j])return -1;41                 if(maz[i][j] == maz[i][k] + maz[k][j])42                 {43                     cnt++;maz[i][j]=-1;44                 }45             }46         }47     }48     return n*(n-1) - cnt ;49 }50 int main()51 {52     #ifndef ONLINE_JUDGE53     freopen("in","r",stdin);54     #endif55     int T,cas=0;56     scanf("%d",&T);57     while(T--)58     {59         int n;60         scanf("%d",&n);61         memset(maz,0,sizeof(maz));62         for(int i=0;i<n;i++)63             for(int j=0;j<n;j++)64                 scanf("%d",&maz[i][j]);65         int tmp = floyd(n);66         printf("Case %d: ",++cas);67         if(tmp != -1)printf("%d\n",tmp);68         else puts("impossible");69     }70     return 0;71 }