Submission #246716

#	Time	Username	Problem	Language	Result	Execution time	Memory
246716		dantoh000	Potemkin cycle (CEOI15_indcyc)	C++14	50 / 100	28 ms	8540 KiB

indcyc

#include <bits/stdc++.h>
using namespace std;
int n,m;
int id[1005][1005];
int A[1005];
int B[1005];
int vis[100005];
vector<int> ans;
int cycle;
bool dfs(int a, int b){
    vis[id[a][b]] = 2;
    for (int c = 1; c <= n; c++){
        if (c != a && id[b][c] && !id[a][c]){
            if (vis[id[b][c]] == 2){
                cycle = b;
                ans.push_back(b);
                ans.push_back(a);
                return true;
            }
            else if (dfs(b,c)){
                ans.push_back(a);
                if (a == cycle){
                    int s = 0, e = (int)ans.size()-1;
                    for (int x = 0; x < (int)ans.size(); x++){
                        for (int y = x+2; y < (int)ans.size(); y++){
                            if (id[ans[x]][ans[y]] && e-s > y-x){ ///xxx illegal operation
                                //printf("%d -> %d illegal \n",ans[x],ans[y]);
                                /// just take from x to y instead, shorter cycle and guaranteed to be >3 from initial checks
                                s = x, e = y;
                            }
                        }
                    }
                    for (int i = s; i <= e; i++) printf("%d ",ans[i]);
                    exit(0);
                }
                return true;
            }
        }
    }
    vis[id[a][b]] = 1;
    return false;
}
int main(){
    scanf("%d%d",&n,&m);
    for (int i = 1; i <= m; i++){
        scanf("%d%d",&A[i],&B[i]);
        id[B[i]][A[i]] = id[A[i]][B[i]] = i;
    }
    for (int i = 1; i <= m; i++){
        if (vis[i] == 0) {
            assert(id[A[i]][B[i]] == i);
            dfs(A[i],B[i]);
            ans.clear();
        }
    }

    printf("no");
}

Compilation message (stderr)

indcyc.cpp: In function 'int main()':
indcyc.cpp:44:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&n,&m);
     ~~~~~^~~~~~~~~~~~~~
indcyc.cpp:46:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d",&A[i],&B[i]);
         ~~~~~^~~~~~~~~~~~~~~~~~~~

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 10 / 10
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10
• Subtask 10: 0 / 10