June 26, 2022 (LC 6100 counts the number of ways to place houses)

Method ： Dynamic programming

 

class Solution {
    public int countHousePlacements(int n) {
        // state ：dp[i]  Express i Number of ways to place houses when parcels 
        long[] dp = new long[n + 1];
        dp[0] = 1;
        dp[1] = 2;
        for (int i = 2; i <= n; i++) {
            dp[i] = (dp[i - 1] + dp[i - 2]) % 1000000007;
        }
        return (int)(dp[n] * dp[n] % 1000000007);
    }
}