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Strings from an array which are not prefix of any other string

 3 years ago
source link: https://www.geeksforgeeks.org/strings-from-an-array-which-are-not-prefix-of-any-other-string/
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Strings from an array which are not prefix of any other string
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Strings from an array which are not prefix of any other string
  • Difficulty Level : Medium
  • Last Updated : 16 Oct, 2019

Given an array arr[] of strings, the task is to print the strings from the array which are not prefix of any other string from the same array.

Examples:

Input: arr[] = {“apple”, “app”, “there”, “the”, “like”}
Output:
apple
like
there
Here “app” is a prefix of “apple”
Hence, it is not printed and
“the” is a prefix of “there”

Input: arr[] = {“a”, “aa”, “aaa”, “aaaa”}
Output:
aaaa

Naive approach: For every string of the array, we check if it is prefix of any other string. If it is then don’t display it.

Efficient approach: We pick strings from array one by one and insert it into Trie. Then there are two cases for the insertion of the string:

  1. While inserting if we found that the picked string is a prefix of an already inserted string then we don’t insert this string into the Trie.
  2. If a prefix is inserted first into the Trie and afterwards we find that the string is a prefix of some word then we simply make isEndOfWord = false for that particular node.

After constructing the Trie, we traverse it and display all the words in the Trie.

Below is the implementation of the above approach:

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// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
const int ALPHABET_SIZE = 26;
// Trie node
struct TrieNode {
struct TrieNode* children[ALPHABET_SIZE];
// isEndOfWord is true if the node represents
// end of a word
bool isEndOfWord;
};
// Returns new trie node (initialized to NULLs)
struct TrieNode* getNode(void)
{
struct TrieNode* pNode = new TrieNode;
pNode->isEndOfWord = false;
for (int i = 0; i < ALPHABET_SIZE; i++)
pNode->children[i] = NULL;
return pNode;
}
// Function to insert a string into trie
void insert(struct TrieNode* root, string key)
{
struct TrieNode* pCrawl = root;
for (int i = 0; i < key.length(); i++) {
int index = key[i] - 'a';
if (!pCrawl->children[index])
pCrawl->children[index] = getNode();
// While inerting a word make
// each isEndOfWord as false
pCrawl->isEndOfWord = false;
pCrawl = pCrawl->children[index];
}
int i;
// Check if this word is prefix of
// some already inserted word
// If it is then don't insert this word
for (i = 0; i < 26; i++) {
if (pCrawl->children[i]) {
break;
}
}
// If present word is not prefix of
// any other word then insert it
if (i == 26) {
pCrawl->isEndOfWord = true;
}
}
// Function to display words in Trie
void display(struct TrieNode* root, char str[], int level)
{
// If node is leaf node, it indicates end
// of string, so a null character is added
// and string is displayed
if (root->isEndOfWord) {
str[level] = '\0';
cout << str << endl;
}
int i;
for (i = 0; i < ALPHABET_SIZE; i++) {
// If NON NULL child is found
// add parent key to str and
// call the display function recursively
// for child node
if (root->children[i]) {
str[level] = i + 'a';
display(root->children[i], str, level + 1);
}
}
}
// Driver code
int main()
{
string keys[] = { "apple", "app", "there",
"the", "like" };
int n = sizeof(keys) / sizeof(string);
struct TrieNode* root = getNode();
// Construct trie
for (int i = 0; i < n; i++)
insert(root, keys[i]);
char str[100];
display(root, str, 0);
return 0;
}
Output: 
apple
like
there

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