Submission #219039

#	Time	Username	Problem	Language	Result	Execution time	Memory
219039		Nightlight	Building 4 (JOI20_building4)	C++14	100 / 100	454 ms	105928 KiB

building4

#include <cstdio>
#include <stdlib.h>
#include <utility>
#include <algorithm>
#define mn first
#define mx second
using namespace std;

int N;
int A[1000005][2];
bool vis[1000005][2];
pair<int, int> dp[1000005][2];

void DFS(int u, int i) {
  if(vis[u][i]) return;
  vis[u][i] = 1;
  int mn = 2000000000, mx = -2000000000;
  if(A[u][i] <= A[u + 1][0]) {
    DFS(u + 1, 0);
    mn = min(dp[u + 1][0].mn + 1, mn);
    mx = max(dp[u + 1][0].mx + 1, mx);
  }
  if(A[u][i] <= A[u + 1][1]) {
    DFS(u + 1, 1);
    mn = min(dp[u + 1][1].mn, mn);
    mx = max(dp[u + 1][1].mx, mx);
  } 
  dp[u][i] = make_pair(mn, mx);
}

void backtrack() {
  if(dp[0][0] == make_pair(2000000000, -2000000000) || dp[0][0].mn > N >> 1 || dp[0][0].mx < N >> 1) {
    puts("-1");
    exit(0);
  }
  int last = 0, cur = N >> 1;
  for(int i = 0; i < N; i++) {
    if(A[i][last] <= A[i + 1][0] && dp[i + 1][0].mn <= cur - 1 && cur - 1 <= dp[i + 1][0].mx) {
      last = 0; cur--;
      putchar('A');
      continue;
    }
    last = 1;
    putchar('B');
  }
}

int main() {
  scanf("%d", &N);
  N <<= 1;
  for(int i = 1; i <= N; i++) {
    scanf("%d", &A[i][0]);
  }
  for(int i = 1; i <= N; i++) {
    scanf("%d", &A[i][1]);
  }
  vis[N][0] = 1, vis[N][1] = 1;
  dp[N][0] = make_pair(0, 0), dp[N][1] = make_pair(0, 0);
  DFS(0, 0);
  backtrack();
}

Compilation message (stderr)

building4.cpp: In function 'int main()':
building4.cpp:49:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &N);
   ~~~~~^~~~~~~~~~
building4.cpp:52:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &A[i][0]);
     ~~~~~^~~~~~~~~~~~~~~~
building4.cpp:55:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &A[i][1]);
     ~~~~~^~~~~~~~~~~~~~~~

• Subtask 1: 11 / 11
• Subtask 2: 89 / 89