Leetcode: dynamic planning template

1. Count rabbits

There is a rabbit , From the day after birth 3 A rabbit has been born every month since last month , The little rabbit grows to the third month and gives birth to another rabbit every month , If the rabbits don't die , Ask the total number of rabbits per month ？

Let's assume that No n-2 When I was six months old dp[n-2] A rabbit , The first n-1 When I was six months old dp[n-1] A rabbit , So the first n How many rabbits are there in a month ？ The first n A month old rabbit must have a first n-1 A month old rabbit came , So at least dp[n-1] A rabbit , But at the same time , Rabbits born two months old will have another rabbit . How many rabbits are there two months old ？ The rabbit that is pushed forward for two months is the rabbit that is currently born for two months （ Nonsense Literature ）, So the number of rabbits born two months is dp[n-2] individual , These rabbits will already be included dp[n-1] In , But they will also have dp[n-2] A rabbit , therefore dp[n]=dp[n-1]+dp[n-2].

Rabbits two months ago will have a rabbit , How many rabbits were there two months ago ？ The answer is dp[n-2], Rabbits one month ago will also be classified as next month