BOJ 2482: 색상환

작성일

https://www.acmicpc.net/problem/2482

  • 3월동안 210문제 풀기 (9/210)
  • 어거지 DP로 어떻게든 풀었음
  • 이건 규칙을 제대로 찾아서 더 효율적으로 풀어봐야함.
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#include <bits/stdc++.h>
using namespace std;

typedef long long LL;
const LL MOD = 1e9+3;
int N, K;
LL dp[2][2][1001][502];

LL go(int first, int prev, int cur, int remain) {
  if(N-cur < (remain-!first)*2) return 0;
  if(remain == 0) return 1;
  if(cur == N-1) {
    if(remain == 1 && first == 0 && prev == 0) return 1;
    else return 0;
  }
  if(dp[first][prev][cur][remain] != -1) return dp[first][prev][cur][remain];

  LL ans = 0;
  if(!prev) ans = (ans + go(first, 1, cur+1, remain-1)) % MOD;
  ans = (ans + go(first, 0, cur+1, remain)) % MOD;

  return dp[first][prev][cur][remain] = ans;
}


int main() {
  cin >> N >> K;
  memset(dp, -1, sizeof(dp));
  LL ans = 0;
  ans = (ans + go(1, 1, 1, K-1)) % MOD;
  ans = (ans + go(0, 0, 1, K)) % MOD;
  cout << ans;
}