1641. Count Sorted Vowel Strings | LeetCode Solution
Given an integer n
, return the number of strings of length n
that consist only of vowels (a
, e
, i
, o
, u
) and are lexicographically sorted.
A string s
is lexicographically sorted if for all valid i
, s[i]
is the same as or comes before s[i+1]
in the alphabet.
Example 1:
Input: n = 1
Output: 5
Explanation: The 5 sorted strings that consist of vowels only are ["a","e","i","o","u"].
Example 2:
Input: n = 2
Output: 15
Explanation: The 15 sorted strings that consist of vowels only are
["aa","ae","ai","ao","au","ee","ei","eo","eu","ii","io","iu","oo","ou","uu"].
Note that "ea" is not a valid string since 'e' comes after 'a' in the alphabet.
Example 3:
Input: n = 33
Output: 66045
Constraints:
1 <= n <= 50
class Solution {public: int countVowelStrings(int n) { vector<int>dp(5,1); int ans=0; while(--n){ for(int i=3; i>=0; i--){ dp[i]+=dp[i+1]; } } for(auto x:dp)ans+=x; return ans; }};
Given an integer n
, return the number of strings of length n
that consist only of vowels (a
, e
, i
, o
, u
) and are lexicographically sorted.
A string s
is lexicographically sorted if for all valid i
, s[i]
is the same as or comes before s[i+1]
in the alphabet.
Example 1:
Input: n = 1
Output: 5
Explanation: The 5 sorted strings that consist of vowels only are ["a","e","i","o","u"].
Example 2:
Input: n = 2 Output: 15 Explanation: The 15 sorted strings that consist of vowels only are ["aa","ae","ai","ao","au","ee","ei","eo","eu","ii","io","iu","oo","ou","uu"]. Note that "ea" is not a valid string since 'e' comes after 'a' in the alphabet.
Example 3:
Input: n = 33 Output: 66045
Constraints:
1 <= n <= 50
class Solution {
public:
int countVowelStrings(int n) {
vector<int>dp(5,1);
int ans=0;
while(--n){
for(int i=3; i>=0; i--){
dp[i]+=dp[i+1];
}
}
for(auto x:dp)ans+=x;
return ans;
}
};
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