给定一个字符串，返回所有可能的以元音开头并以辅音结尾的子序列。字符串是给定字符串的子序列，它是通过删除给定字符串的某些字符而不改变其顺序而生成的。
例子：
Input : 'abc'
Output : ab, ac, abc
Input : 'aab'
Output : ab, aab
问题来源：Yatra.com 面试经历 | 7套
算法说明：
Step 1: Iterate over the entire String
Step 2: check if the ith character for vowel
Step 3: If true iterate the string from the end,
if false move to next iteration
Step 4: check the jth character for consonent
if false move to next iteration
if true perform the following
Step 5: Add the substring starting at index i and
ending at index j to the hastset.
Step 6: Iterate over the substring drop each character
and recur to generate all its subString
C++
// C++ program to generate all the subse-quence
// starting with vowel and ending with consonant.
#include
using namespace std;
// Set to store all the subsequences
set st;
// Utility method to check vowel
bool isVowel(char c)
{
return (c == 'a' or c == 'e' or
c == 'i' or c == 'o' or
c == 'u');
}
// Utility method to check consonant
bool isConsonant(char c)
{
return !isVowel(c);
}
// It computes all the possible substring that
// starts with vowel and end with consonent
void subsequence(string str)
{
// iterate over the entire string
for (int i = 0; i < str.length(); i++)
{
// test ith character for vowel
if (isVowel(str[i]))
{
// if the ith character is vowel
// iterate from end of the string
// and check for consonant.
for (int j = str.length() - 1; j >= i; j--)
{
// test jth character for consonant.
if (isConsonant(str[j]))
{
// once we get a consonant add it to
// the hashset
string str_sub = str.substr(i, j + 1);
st.insert(str_sub);
// drop each character of the substring
// and recur to generate all subsequence
// of the substring
for (int k = 1; k < str_sub.length() - 1; k++)
{
string sb = str_sub;
sb.erase(sb.begin() + k);
subsequence(sb);
}
}
}
}
}
}
// Driver Code
int main()
{
string s = "xabcef";
subsequence(s);
for (auto i : st)
cout << i << " ";
cout << endl;
return 0;
}
// This code is contributed by
// sanjeev2552 Java
// Java Program to generate all the subsequence
// starting with vowel and ending with consonant.
import java.util.HashSet;
public class Subsequence {
// Set to store all the subsequences
static HashSet st = new HashSet<>();
// It computes all the possible substring that
// starts with vowel and end with consonent
static void subsequence(String str)
{
// iterate over the entire string
for (int i = 0; i < str.length(); i++) {
// test ith character for vowel
if (isVowel(str.charAt(i))) {
// if the ith character is vowel
// iterate from end of the string
// and check for consonant.
for (int j = (str.length() - 1); j >= i; j--) {
// test jth character for consonant.
if (isConsonant(str.charAt((j)))) {
// once we get a consonant add it to
// the hashset
String str_sub = str.substring(i, j + 1);
st.add(str_sub);
// drop each character of the substring
// and recur to generate all subsequence
// of the substring
for (int k = 1; k < str_sub.length() - 1; k++) {
StringBuffer sb = new StringBuffer(str_sub);
sb.deleteCharAt(k);
subsequence(sb.toString());
}
}
}
}
}
}
// Utility method to check vowel
static boolean isVowel(char c)
{
return (c == 'a' || c == 'e' || c == 'i' || c == 'o'
|| c == 'u');
}
// Utility method to check consonant
static boolean isConsonant(char c)
{
return !isVowel(c);
}
// Driver code
public static void main(String[] args)
{
String s = "xabcef";
subsequence(s);
System.out.println(st);
}
} C#
// C# Program to generate all the subsequence
// starting with vowel and ending with consonant.
using System;
using System.Collections.Generic;
using System.Text;
class Subsequence
{
// Set to store all the subsequences
static HashSet st = new HashSet();
// It computes all the possible substring that
// starts with vowel and end with consonent
static void subsequence(String str)
{
// iterate over the entire string
for (int i = 0; i < str.Length; i++)
{
// test ith character for vowel
if (isVowel(str[i]))
{
// if the ith character is vowel
// iterate from end of the string
// and check for consonant.
for (int j = (str.Length - 1); j >= i; j--)
{
// test jth character for consonant.
if (isConsonant(str[j]))
{
// once we get a consonant add it to
// the hashset
String str_sub = str.Substring(i, j -i + 1);
st.Add(str_sub);
// drop each character of the substring
// and recur to generate all subsequence
// of the substring
for (int k = 1; k < str_sub.Length - 1; k++)
{
StringBuilder sb = new StringBuilder(str_sub);
sb.Remove(k, 1);
subsequence(sb.ToString());
}
}
}
}
}
}
// Utility method to check vowel
static bool isVowel(char c)
{
return (c == 'a' || c == 'e' || c == 'i' || c == 'o'
|| c == 'u');
}
// Utility method to check consonant
static bool isConsonant(char c)
{
return !isVowel(c);
}
// Driver code
public static void Main(String[] args)
{
String s = "xabcef";
subsequence(s);
foreach(String str in st)
Console.Write(str + ", ");
}
}
// This code is contributed by Rajput-Ji 输出：
[ef, ab, ac, aef, abc, abf, af, acf, abcef, abcf, acef, abef]
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