2559_CountVowelStringsinRanges - a920604a/leetcode GitHub Wiki

categories: leetcode comments: false tags:

  • Prefix Sum title: 2559. Count Vowel Strings in Ranges

problem

solution

C++ solution

class Solution {
public:
    unordered_set<char> vowels = {'a', 'e', 'i', 'o', 'u'};
    bool checkStartAndEndVowel(string word){
        if(word == "") return false;
        bool ret = vowels.count(word.front())==1;
        if(!ret) return false;
        return ret && vowels.count(word.back())==1;
    }
    vector<int> vowelStrings(vector<string>& words, vector<vector<int>>& queries) {
        int n = words.size(), q = queries.size();
        vector<bool> filters(n, false);
        vector<int> prefixSum(n+1, 0);
        // prefix sum
        //      1    0   1   1   1
        // 0    1    1   2   3   4
        vector<int> ret(q, 0);
        for(int i= 0 ;i<n;++i) filters[i] = checkStartAndEndVowel(words[i]);
        int tmp = 0;
        for(int i=0;i<n;++i){
            tmp += (filters[i]);
            prefixSum[i+1] = tmp;
        }
        for(int i=0;i<q ; ++i){
            ret[i] = prefixSum[queries[i][1]+1] - prefixSum[queries[i][0]];
        }
        return ret;
    }
};

Python solution

class Solution:
    def vowelStrings(self, words: List[str], queries: List[List[int]]) -> List[int]:
        s = {'a', 'e', 'i', 'o', 'u'}
        filters = [1 if word[0] in s and word[-1] in s else 0 for word in words]
        prefix = [0]
        for f in filters:
            prefix.append(f + prefix[-1])
        ret = list()
        for q in queries:
            ret.append( prefix[q[1]+1] - prefix[q[0]])
        return ret

analysis

  • time complexity O(n + m), m = queries length, n = words length
  • space complexity O(n + m)

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