2559. 统计范围内的元音字符串数 (opens new window)

1.前缀和

统计前i个字符里元音字符的个数。那么查询第 i 个字符到第 j 个字符的元音字符串的数目计算如下：num = prefix [ j ] - prefix[ i ]

class Solution {
    public int[] vowelStrings(String[] words, int[][] queries) {
        int[] prefix=new int[words.length];
        for(int i=0;i<words.length;i++){
            if((words[i].startsWith("a")||words[i].startsWith("e")||words[i].startsWith("i")
            ||words[i].startsWith("o")||words[i].startsWith("u"))&&
            (words[i].endsWith("a")||words[i].endsWith("e")||words[i].endsWith("i")
            ||words[i].endsWith("o")||words[i].endsWith("u"))){
                if(i==0) prefix[i]=1;
                else
                prefix[i]=prefix[i-1]+1;
                continue;
            }
            if(i>0)
            prefix[i]=prefix[i-1];
        }
        int[] res=new int[queries.length];
        for(int i=0;i<queries.length;i++){
            
            res[i]=queries[i][0]==0?prefix[queries[i][1]]:prefix[queries[i][1]]-prefix[queries[i][0]-1];
        }
        return res;
    }
}