Submission #261660

#	Time	Username	Problem	Language	Result	Execution time	Memory
261660		tincamatei	Sailing Race (CEOI12_race)	C++14	60 / 100	3072 ms	6472 KiB

race

#include <bits/stdc++.h>

const int MAX_N = 500;

bool graph[MAX_N][MAX_N];
int asc[MAX_N][MAX_N], desc[MAX_N][MAX_N];
int asc_path[MAX_N][MAX_N], desc_path[MAX_N][MAX_N];
int first_node[MAX_N][MAX_N], last_node[MAX_N][MAX_N];

int N;
static inline int next_node(int v, int k = 1) { return (v + k) % N; }
static inline int prev_node(int v, int k = 1) { return (v + N - k) % N; }

int main() {
  int K;

  scanf("%d%d", &N, &K);

  for(int i = 0; i < N; ++i) {
    int t;
    scanf("%d", &t);
    while(t != 0) {
      graph[i][t - 1] = true;
      scanf("%d", &t);
    }

    asc_path[i][i] = desc_path[i][i] = 0;
  }
  
  for(int i = 0; i < N; ++i)
    for(int j = 0; j < N; ++j)
      first_node[i][j] = last_node[i][j] = -1;

  for(int len = 2; len <= N; ++len) {
    for(int i = 0; i < N; ++i) {
      int j = next_node(i, len - 1), k = i;
      
      asc_path[i][j] = -1;
      do {
        k = next_node(k);
        if(graph[i][k]) {
          asc[i][j] = std::max(asc[i][j], 1 + std::max(asc[k][j], desc[k][next_node(i)]));
          if(asc_path[k][j] != -1)
            asc_path[i][j] = std::max(asc_path[i][j], 1 + asc_path[k][j]);
        }
      } while(k != j);

      j = prev_node(i, len - 1);
      k = i;
      
      desc_path[i][j] = -1;
      do {
        k = prev_node(k);
        if(graph[i][k]) {
          desc[i][j] = std::max(desc[i][j], 1 + std::max(desc[k][j], asc[k][prev_node(i)]));
          if(desc_path[k][j] != -1)
            desc_path[i][j] = std::max(desc_path[i][j], 1 + desc_path[k][j]);
        }
      } while(k != j);
    }
  }

  int best_len = 0, start_path = 0;

  for(int i = 0; i < N; ++i) {
    int ii = prev_node(i);

    if(asc[i][ii] > best_len) {
      best_len = asc[i][ii];
      start_path = i;
    }

    ii = next_node(i);
    if(desc[i][ii] > best_len) {
      best_len = desc[i][ii];
      start_path = i;
    }
  }
  
  if(K == 1 && N >= 4) {
    for(int k = 0; k < N; ++k) {
      for(int len = 1; len <= N; ++len) {
        for(int i = 0; i < N; ++i) {
          int j = next_node(i, len - 1);
          if(graph[i][k]) {
            first_node[i][j] = i;
            last_node[i][j] = j;
          } else if(len > 1) {
            first_node[i][j] = first_node[next_node(i)][j];
            last_node[i][j] = last_node[i][prev_node(j)];
          } else {
            first_node[i][j] = last_node[i][j] = -1;
          }
        }
      }
      
      for(int i = prev_node(k); i != next_node(k); i = prev_node(i))
        for(int j = next_node(k); j != prev_node(i); j = next_node(j)) {
          // last_node  -> k -> i -> j -> ()
          int root = last_node[next_node(j)][prev_node(i)];
          if(graph[i][j] && root != -1 && desc_path[k][i] != -1) {
            int path_len = 1 + desc_path[k][i] + 1 +
              std::max(
                asc[j][prev_node(root)],
                desc[j][next_node(k)]
              );
          
            if(path_len > best_len) {
              best_len = path_len;
              start_path = root;
            }
          }

          // first_node -> k -> j -> i
          root = first_node[next_node(j)][prev_node(i)];
          if(graph[j][i] && root != -1 && asc_path[k][j] != -1) {
            int path_len = 1 + asc_path[k][j] + 1 +
              std::max(
                asc[i][prev_node(k)],
                desc[i][next_node(root)]
              );
            
            if(path_len > best_len) {
              best_len = path_len;
              start_path = root;
            }
          }
        }
    }
  }

  printf("%d\n%d", best_len, start_path + 1);

  return 0;
}

Compilation message (stderr)

race.cpp: In function 'int main()':
race.cpp:17:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d", &N, &K);
   ~~~~~^~~~~~~~~~~~~~~~
race.cpp:21:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &t);
     ~~~~~^~~~~~~~~~
race.cpp:24:12: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
       scanf("%d", &t);
       ~~~~~^~~~~~~~~~

• Subtask 1: 60 / 100