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# Length of longest common subsequence containing vowels

Given two strings X and Y of length m and n respectively. The problem is to find the length of the longest common subsequence of strings X and Y which contains all vowel characters.

Examples:

```Input : X = "aieef"
Y = "klaief"
Output : aie

Input : X = "geeksforgeeks"
Y = "feroeeks"
Output : eoee```

Naive Approach: Generate all subsequences of both given sequences and find the longest matching subsequence which contains all vowel characters. This solution is exponential in term of time complexity.

Efficient Approach (Dynamic Programming): This approach is a variation to Longest Common Subsequence | DP-4 problem.

The difference in this post is just that the common subsequence characters must all be vowels.

Implementation:

## C++

 `// C++ implementation to find the length of longest common``// subsequence which contains all vowel characters``#include ` `using` `namespace` `std;` `// function to check whether 'ch'``// is a vowel or not``bool` `isVowel(``char` `ch)``{``    ``if` `(ch == ``'a'` `|| ch == ``'e'` `|| ch == ``'i'``        ``|| ch == ``'o'` `|| ch == ``'u'``)``        ``return` `true``;``    ``return` `false``;``}` `// function to find the length of longest common subsequence``// which contains all vowel characters``int` `lcs(``char``* X, ``char``* Y, ``int` `m, ``int` `n)``{``    ``int` `L[m + 1][n + 1];``    ``int` `i, j;` `    ``// Following steps build L[m+1][n+1] in bottom up fashion. Note``    ``// that L[i][j] contains length of LCS of X[0..i-1] and Y[0..j-1]``    ``for` `(i = 0; i <= m; i++) {``        ``for` `(j = 0; j <= n; j++) {``            ``if` `(i == 0 || j == 0)``                ``L[i][j] = 0;` `            ``else` `if` `((X[i - 1] == Y[j - 1]) && isVowel(X[i - 1]))``                ``L[i][j] = L[i - 1][j - 1] + 1;` `            ``else``                ``L[i][j] = max(L[i - 1][j], L[i][j - 1]);``        ``}``    ``}` `    ``// L[m][n] contains length of LCS for X[0..n-1] and Y[0..m-1]``    ``// which contains all vowel characters``    ``return` `L[m][n];``}` `// Driver program to test above``int` `main()``{``    ``char` `X[] = ``"aieef"``;``    ``char` `Y[] = ``"klaief"``;` `    ``int` `m = ``strlen``(X);``    ``int` `n = ``strlen``(Y);` `    ``cout << ``"Length of LCS = "``         ``<< lcs(X, Y, m, n);` `    ``return` `0;``}`

## Java

 `// Java implementation to find the``// length of longest common subsequence``// which contains all vowel characters``class` `GFG``{` `// function to check whether 'ch'``// is a vowel or not``static` `boolean` `isVowel(``char` `ch)``{``    ``if` `(ch == ``'a'` `|| ch == ``'e'` `||``        ``ch == ``'i'` `|| ch == ``'o'` `||``        ``ch == ``'u'``)``        ``return` `true``;``    ``return` `false``;``}` `// function to find the length of``// longest common subsequence which``// contains all vowel characters``static` `int` `lcs(String X, String Y,``               ``int` `m, ``int` `n)``{``    ``int` `L[][] = ``new` `int``[m + ``1``][n + ``1``];``    ``int` `i, j;` `    ``// Following steps build L[m+1][n+1]``    ``// in bottom up fashion. Note that``    ``// L[i][j] contains length of LCS of``    ``// X[0..i-1] and Y[0..j-1]``    ``for` `(i = ``0``; i <= m; i++)``    ``{``        ``for` `(j = ``0``; j <= n; j++)``        ``{``            ``if` `(i == ``0` `|| j == ``0``)``                ``L[i][j] = ``0``;` `            ``else` `if` `((X.charAt(i - ``1``) == Y.charAt(j - ``1``)) &&``                                ``isVowel(X.charAt(i - ``1``)))``                ``L[i][j] = L[i - ``1``][j - ``1``] + ``1``;` `            ``else``                ``L[i][j] = Math.max(L[i - ``1``][j],``                                   ``L[i][j - ``1``]);``        ``}``    ``}` `    ``// L[m][n] contains length of LCS``    ``// for X[0..n-1] and Y[0..m-1]``    ``// which contains all vowel characters``    ``return` `L[m][n];``}` `// Driver Code``public` `static` `void` `main(String[] args)``{``    ``String X = ``"aieef"``;``    ``String Y = ``"klaief"``;` `    ``int` `m = X.length();``    ``int` `n = Y.length();` `    ``System.out.println(``"Length of LCS = "` `+``                          ``lcs(X, Y, m, n));``}``}` `// This code is contributed by Bilal`

## Python3

 `# Python3 implementation to find the``# length of longest common subsequence``# which contains all vowel characters` `# function to check whether 'ch'``# is a vowel or not``def` `isVowel(ch):``    ``if` `(ch ``=``=` `'a'` `or` `ch ``=``=` `'e'` `or``        ``ch ``=``=` `'i'``or` `ch ``=``=` `'o'` `or``        ``ch ``=``=` `'u'``):``        ``return` `True``    ``return` `False` `# function to find the length of longest``# common subsequence which contains all``# vowel characters``def` `lcs(X, Y, m, n):` `    ``L ``=` `[[``0` `for` `i ``in` `range``(n ``+` `1``)]``            ``for` `j ``in` `range``(m ``+` `1``)]``    ``i, j ``=` `0``, ``0`` ` `    ``# Following steps build L[m+1][n+1] in``    ``# bottom up fashion. Note that L[i][j]``    ``# contains length of LCS of X[0..i-1]``    ``# and Y[0..j-1]``    ``for` `i ``in` `range``(m ``+` `1``):``        ``for` `j ``in` `range``(n ``+` `1``):``            ``if` `(i ``=``=` `0` `or` `j ``=``=` `0``):``                ``L[i][j] ``=` `0``            ``elif` `((X[i ``-` `1``] ``=``=` `Y[j ``-` `1``]) ``and``                      ``isVowel(X[i ``-` `1``])):``                ``L[i][j] ``=` `L[i ``-` `1``][j ``-` `1``] ``+` `1``            ``else``:``                ``L[i][j] ``=` `max``(L[i ``-` `1``][j],``                              ``L[i][j ``-` `1``])``    ` `    ``# L[m][n] contains length of LCS for``    ``# X[0..n-1] and Y[0..m-1] which``    ``# contains all vowel characters``    ``return` `L[m][n]` `# Driver Code``X ``=` `"aieef"``Y ``=` `"klaief"` `m ``=` `len``(X)``n ``=` `len``(Y)` `print``(``"Length of LCS ="``, lcs(X, Y, m, n))` `# This code is contributed by Mohit Kumar`

## C#

 `// C# implementation to find the``// length of longest common subsequence``// which contains all vowel characters``using` `System;` `class` `GFG``{` `// function to check whether``// 'ch' is a vowel or not``static` `int` `isVowel(``char` `ch)``{``    ``if` `(ch == ``'a'` `|| ch == ``'e'` `||``        ``ch == ``'i'` `|| ch == ``'o'` `||``        ``ch == ``'u'``)``        ``return` `1;``    ``return` `0;``}` `// find max value``static` `int` `max(``int` `a, ``int` `b)``{``    ``return` `(a > b) ? a : b;``}` `// function to find the length of``// longest common subsequence which``// contains all vowel characters``static` `int` `lcs(String X, String Y,``               ``int` `m, ``int` `n)``{``    ``int` `[,]L = ``new` `int``[m + 1, n + 1];``    ``int` `i, j;` `    ``// Following steps build L[m+1,n+1]``    ``// in bottom up fashion. Note that``    ``// L[i,j] contains length of LCS of``    ``// X[0..i-1] and Y[0..j-1]``    ``for` `(i = 0; i <= m; i++)``    ``{``        ``for` `(j = 0; j <= n; j++)``        ``{``            ``if` `(i == 0 || j == 0)``                ``L[i, j] = 0;` `            ``else` `if` `((X[i - 1] == Y[j - 1]) &&``                    ``isVowel(X[i - 1]) == 1)``                ``L[i, j] = L[i - 1, j - 1] + 1;`` ` `            ``else``                ``L[i, j] = max(L[i - 1, j],``                              ``L[i, j - 1]);``        ``}``    ``}` `    ``// L[m,n] contains length of LCS``    ``// for X[0..n-1] and Y[0..m-1]``    ``// which contains all vowel characters``    ``return` `L[m, n];``}` `// Driver Code``static` `public` `void` `Main(String []args)``{``    ``String X = ``"aieef"``;``    ``String Y = ``"klaief"``;` `    ``int` `m = X.Length;``    ``int` `n = Y.Length;` `    ``Console.WriteLine(``"Length of LCS = "` `+``                         ``lcs(X, Y, m, n));``}``}` `// This code is contributed by Arnab Kundu`

## PHP

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## Javascript

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Output

`Length of LCS = 3`

Complexity Analysis:

• Time Complexity: O(m*n).
• Auxiliary Space: O(m*n).

Efficient approach : Space optimization

In previous approach the current value dp[i][j] is only depend upon the current and previous row values of DP. So to optimize the space complexity we use a single 1D array to store the computations.

Implementation:

## C++

 `// C++ implementation to find the length of longest common``// subsequence which contains all vowel characters``#include ``using` `namespace` `std;` `// function to check whether 'ch'``// is a vowel or not``bool` `isVowel(``char` `ch)``{``    ``if` `(ch == ``'a'` `|| ch == ``'e'` `|| ch == ``'i'` `|| ch == ``'o'` `|| ch == ``'u'``)``        ``return` `true``;``    ``return` `false``;``}` `// function to find the length of longest common subsequence``// which contains all vowel characters``int` `lcs(``char``* X, ``char``* Y, ``int` `m, ``int` `n)``{  ``        ` `    ``// initialize vector dp to store``    ``// computations of subproblems``    ``vector<``int``> dp(n + 1, 0);``    ` `    ``// iterating over subproblems to get the``    ``// current value from previous computations``    ``for` `(``int` `i = 1; i <= m; i++) {``        ``// to store just previous value``        ``int` `prev = 0;``        ``for` `(``int` `j = 1; j <= n; j++) {``            ` `            ``// current value``            ``int` `curr = dp[j];``            ``if` `((X[i - 1] == Y[j - 1]) && isVowel(X[i - 1]))``                ``dp[j] = prev + 1;``            ``else``                ``dp[j] = max(dp[j], dp[j - 1]);``                ` `            ``// assigning values to iterate further``            ``prev = curr;``        ``}``    ``}``    ` `    ``// return answer``    ``return` `dp[n];``}` `// Driver Code``int` `main()``{``    ``char` `X[] = ``"aieef"``;``    ``char` `Y[] = ``"klaief"``;` `    ``int` `m = ``strlen``(X);``    ``int` `n = ``strlen``(Y);` `    ``cout << ``"Length of LCS = "` `<< lcs(X, Y, m, n);` `    ``return` `0;``}`

Output

`Length of LCS = 3`

Time Complexity: O(m*n).
Auxiliary Space: O(n).

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