ETC | Yein Yi

Setting up the recurrence is essential for every problem

Ezreal goes mid first gg - 20500

Problem 20500: Ezreal goes mid first gg

You can store the number itself instead of the remainder.
But it's probably better to solve it by storing the remainder.
Handling the inverse operation of the remainder can be important in this problem.

let FIVE = 1, ONE = 0, MOD = 1_000_000_007
let N = Int(readLine()!)!
var dp = [[[Int]]](repeating:[[Int]](repeating:[Int](repeating:0,count:2),count:3),count:N+1)

dp[1][1][ONE] = 1
dp[1][2][FIVE] = 1

for i in 1..<N {
    for j in 0...2 {
        dp[i+1][(j+1)%3][ONE] = (dp[i+1][(j+1)%3][ONE] + dp[i][j][ONE]) % MOD
        dp[i+1][(j+1)%3][ONE] = (dp[i+1][(j+1)%3][ONE] + dp[i][j][FIVE]) % MOD
        dp[i+1][(j+5)%3][FIVE] = (dp[i+1][(j+5)%3][FIVE] + dp[i][j][ONE]) % MOD
        dp[i+1][(j+5)%3][FIVE] = (dp[i+1][(j+5)%3][FIVE] + dp[i][j][FIVE]) % MOD
    }
}

print(dp[N][0][FIVE])

Problem 16500: String Check

Problem 1915: Largest Square

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