題目：198. House Robber

連結：https://leetcode.com/problems/house-robber/description/

• 等級：Medium

class Solution {
    public int rob(int[] nums) {
        int prev = nums[0],prev2=0,curr;
        for(int i=1;i<nums.length;i++)
        {
            int notSkippingCurrIDX = prev2 + nums[i];
            int skippingCurrIDX = prev;
            curr = Math.max(notSkippingCurrIDX,skippingCurrIDX);
            prev2 = prev;
            prev = curr;
        }
        return prev;

    }
}

• Time complexity: O(n)
• Space complexity: O(1)

題目：1641. Count Sorted Vowel Strings

連結：https://leetcode.com/problems/count-sorted-vowel-strings/description/

• 等級：Medium

解題思路

1. 最初所有元音都是 1
2. 然後每一步母音將依照a = a+e+i+o+u, e = e+i+o+u, i=i+o+u.. 等等，
3. 直到我們達到給定的數字重複這個過程

a -> aa, ae, ai, ao, au
e -> ee, ei, eo, eu
i -> ii, io, iu
0 -> oo, ou
u -> uu

class Solution {
	int a=1, e=1, i=1, o=1, u=1;
    public int countVowelStrings(int n) { 
    	for(int j=1; j<n; j++){
        	increment();
        }
    	return a+e+i+o+u;
    }

    private void increment() {
		a = a+e+i+o+u;
		e = e+i+o+u;
		i = i+o+u;
		o = o+u;
	}
}

• Time complexity: O(n)
• Space complexity: O(1)