动态规划

• 70. 爬楼梯
• 1220. 统计元音字母序列的数目

70. 爬楼梯

Leetcode

class Solution {
    public int climbStairs(int n) {
        int a = 1, b = 2, w; // 爬 1、2 级的方案数
        while (--n > 0){
            w = b;
            b = a + b;
            a = w;
        }
        return a;
    }
}

1220. 统计元音字母序列的数目

Leetcode

class Solution {
    public int countVowelPermutation(int n) {
        long mod = 1000000007;
        long a = 1, e = 1, i = 1, o = 1, u = 1;
        long a1, e1, i1, o1, u1;
        while(--n > 0){
            a1 = (u + e + i) % mod;
            e1 = (a + i) % mod;
            i1 = (e + o) % mod;
            o1 = i % mod;
            u1 = (i + o) % mod;
            a = a1; e = e1; i = i1; o = o1; u = u1;
        }
        return (int)((a + e + i + o + u) % mod); 
    }
}