# Find largest word in dictionary by deleting some characters of given string

Giving a dictionary and a string ‘str’, find the longest string in dictionary which can be formed by deleting some characters of the given ‘str’.

Examples:

```Input : dict = {"ale", "apple", "monkey", "plea"}
str = "abpcplea"
Output : apple

Input  : dict = {"pintu", "geeksfor", "geeksgeeks",
" forgeek"}
str = "geeksforgeeks"
Output : geeksgeeks
```

## Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

This problem reduces to finding if a string is subsequence of another string or not. We traverse all dictionary words and for every word, we check if it is subsequence of given string and is largest of all such words. We finally return the longest word with given string as subsequence.

Below c++ implementation of above idea

```// C++ program to find largest word in Dictionary
// by deleting some characters of given string
#include <bits/stdc++.h>
using namespace std;

// Returns true if str1[] is a subsequence of str2[].
// m is length of str1 and n is length of str2
bool isSubSequence(string str1, string str2)
{
int m = str1.length(), n = str2.length();

int j = 0; // For index of str1 (or subsequence

// Traverse str2 and str1, and compare current
// character of str2 with first unmatched char
// of str1, if matched then move ahead in str1
for (int i=0; i<n&&j<m; i++)
if (str1[j] == str2[i])
j++;

// If all characters of str1 were found in str2
return (j==m);
}

// Returns the longest string in dictionary which is a
// subsequence of str.
string findLongestString(vector <string > dict, string str)
{
string result = "";
int length = 0;

// Traverse through all words of dictionary
for (string word : dict)
{
// If current word is subsequence of str and is largest
// such word so far.
if (length < word.length() && isSubSequence(word, str))
{
result = word;
length = word.length();
}
}

// Return longest string
return result;
}

// Driver program to test above function
int main()
{
vector <string > dict = {"ale", "apple", "monkey", "plea"};
string str = "abpcplea" ;
cout << findLongestString(dict, str) << endl;
return 0;
}
```

Output:

```apple
```

Time Complexity : O(N*K*n) Here N is the length of dictionary and n is the length of given string ‘str’ and K – maximum length of words in the dictionary.

Auxiliary Space : O(1)

This article is contributed by Nishant Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

# GATE CS Corner    Company Wise Coding Practice

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.
2.1 Average Difficulty : 2.1/5.0
Based on 12 vote(s)