𝗧𝗵𝗲 𝗙𝗶𝗿𝘀𝘁 𝗦𝘁𝗿𝗲𝗮𝗸 𝗼𝗻 𝗟𝗲𝗲𝘁𝗖𝗼𝗱𝗲

class Solution { public int checkRecord(int n) { final int MOD = 1000000007; int[][] dpCurrState = new int[2][3]; int[][] dpNextState = new int[2][3]; dpCurrState[0][0] = 1; for (int len = 0; len < n; len++) { for (int i = 0; i < 2; i++) { Arrays.fill(dpNextState[i], 0); } for (int totalAbsences = 0; totalAbsences < 2; totalAbsences++) { for (int consecutiveLates = 0; consecutiveLates < 3; consecutiveLates++) { dpNextState[totalAbsences][0] = (dpNextState[totalAbsences][0] + dpCurrState[totalAbsences][consecutiveLates]) % MOD; if (totalAbsences < 1) { dpNextState[totalAbsences + 1][0] = (dpNextState[totalAbsences + 1][0] + dpCurrState[totalAbsences][consecutiveLates]) % MOD; } if (consecutiveLates < 2) { dpNextState[totalAbsences][consecutiveLates + 1] = (dpNextState[totalAbsences][consecutiveLates + 1] + dpCurrState[totalAbsences][consecutiveLates]) % MOD; } } } for (int i = 0; i < 2; i++) { System.arraycopy(dpNextState[i], 0, dpCurrState[i], 0, 3); } } int totalCount = 0; for (int totalAbsences = 0; totalAbsences < 2; totalAbsences++) { for (int consecutiveLates = 0; consecutiveLates < 3; consecutiveLates++) { totalCount = (totalCount + dpCurrState[totalAbsences][consecutiveLates]) % MOD; } } return totalCount; } }