Alien Dictionary problem in dsa

In the field of Data Structures and Algorithms (DSA), the Alien Dictionary Problem is an intriguing riddle that tests our comprehension of language representation and order. This challenge, which is frequently seen in competitive programming and computer science interviews, entails resolving a special ordering dilemma presented by the language of an alien civilization. We shall examine the relevance, variants, and possible solutions of the Alien Dictionary Problem as we delve into its complexities in this article.

Understanding the Alien Dictionary Problem:

Figuring out the right character order in an alien alphabet is the key to solving the Alien Dictionary Problem. An extraterrestrial language may have unusual patterns and ordering in contrast to human languages, which adhere to a set of grammatical rules and structures. Given a list of words in the foreign language, the job is to figure out the correct character order.

Imagine we are handed a sorted dictionary of a foreign language, but we don't know the characters' order. Finding a reasonable order that complies with the provided lexicon is the aim. When additional characters or symbols that are absent from our known languages are included in the alien language, this dilemma becomes much more intriguing.

Significance of the Problem:

The Alien Dictionary Problem is more than just an abstract conundrum; it has practical applications, particularly in the fields of linguistics, cryptography, and natural language processing. Understanding a foreign language's character order can help with more accurate language translation and processing in the field of natural language processing.

Furthermore, the issue is useful in cryptography for developing safe encryption techniques that depend on distinct character sequences. Thus, the Alien Dictionary Problem goes beyond its seemingly linguistic roots to become an important part in building reliable and secure computer systems.

Variations on the Alien Dictionary Problem:

The Alien Dictionary Problem exists in a variety of flavors, each offering a unique set of difficulties, just like many other DSA issues. Determining the character order in an unfamiliar language given a set of words that do not necessarily constitute a sorted dictionary is one frequent variation. This variation introduces another level of complexity, as algorithms must figure out the right order among the seemingly random set of words provided.
An other intriguing variation takes into account if the alien language has cycles. In this case, establishing a linear order may be hard due to circular dependencies within the language. In order to solve this kind of problem, it is necessary to recognize and manage cycles, which involves some principles from graph theory.

Solutions to Alien Dictionary Problem:

The Alien Dictionary Problem can be solved using a variety of algorithms, each of which makes use of unique data structures and techniques. Building a graph with nodes representing characters and directed edges indicating the relative order of characters using the provided words is one such technique. The right order can then be found by using topological sorting, a basic idea in graph theory.
We may represent the relationships between characters using the graph-based technique, which makes it simpler to determine the right order. On the other hand, different edge circumstances need to be handled carefully, like graph cycles, which can be found using depth-first search (DFS) or other cycle detection algorithms.
An easier method would be to look up the dictionary's nearby words and find the first instance of two different characters. Important details regarding the relative sequence of those characters in the alien language are revealed by this pair. It is possible to create a partial character order that can be expanded upon to create a complete order by repeating this procedure for each pair of neighboring words.

C Implementation:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#define MAX_CHARS 26
struct GraphNode {
    int value;
    struct GraphNode* next;
};
struct Graph {
    int vertices;
    struct GraphNode** adjacencyList;
    int* inDegree;
};
struct GraphNode* createNode(int value) {
    struct GraphNode* newNode = (struct GraphNode*)malloc(sizeof(struct GraphNode));
    newNode->value = value;
    newNode->next = NULL;
    return newNode;
}
struct Graph* createGraph(int vertices) {
    struct Graph* graph = (struct Graph*)malloc(sizeof(struct Graph));
    graph->vertices = vertices;
    graph->adjacencyList = (struct GraphNode**)malloc(vertices * sizeof(struct GraphNode*));
    graph->inDegree = (int*)malloc(vertices * sizeof(int));
    for (int i = 0; i < vertices; ++i) {
        graph->adjacencyList[i] = NULL;
        graph->inDegree[i] = 0;
    }
    return graph;
}
void addEdge(struct Graph* graph, int src, int dest) {
    struct GraphNode* newNode = createNode(dest);
    newNode->next = graph->adjacencyList[src];
    graph->adjacencyList[src] = newNode;
    graph->inDegree[dest]++;
}
void topologicalSortUtil(struct Graph* graph, int vertex, bool visited[], int sortedOrder[]) {
    visited[vertex] = true;
    struct GraphNode* adjNode = graph->adjacencyList[vertex];
    while (adjNode != NULL) {
        int adjVertex = adjNode->value;
        if (!visited[adjVertex]) {
            topologicalSortUtil(graph, adjVertex, visited, sortedOrder);
        }
        adjNode = adjNode->next;
    }
    sortedOrder[--vertex] = vertex;
}
void topologicalSort(struct Graph* graph, int sortedOrder[]) {
    bool* visited = (bool*)malloc(graph->vertices * sizeof(bool));
    for (int i = 0; i < graph->vertices; ++i) {
        visited[i] = false;
    }
    int index = graph->vertices;
    for (int i = 0; i < graph->vertices; ++i) {
        if (!visited[i]) {
            topologicalSortUtil(graph, i, visited, sortedOrder);
        }
    }
    free(visited);
}
void printOrder(int sortedOrder[], int n) {
    printf("Order of characters in the alien language: ");
    for (int i = 0; i < n; ++i) {
        printf("%c ", 'a' + sortedOrder[i]);
    }
    printf("\n");
}
void alienDictionary(char* words[], int n) {
    struct Graph* graph = createGraph(MAX_CHARS);
    for (int i = 0; i < n - 1; ++i) {
        char* word1 = words[i];
        char* word2 = words[i + 1];
        int minLength = (int)strlen(word1) < (int)strlen(word2) ? (int)strlen(word1) : (int)strlen(word2);
        for (int j = 0; j < minLength; ++j) {
            if (word1[j] != word2[j]) {
                addEdge(graph, word1[j] - 'a', word2[j] - 'a');
                break;
            }
        }
    }
    int sortedOrder[MAX_CHARS];
    topologicalSort(graph, sortedOrder);
    printOrder(sortedOrder, MAX_CHARS);
    for (int i = 0; i < MAX_CHARS; ++i) {
        struct GraphNode* current = graph->adjacencyList[i];
        while (current != NULL) {
            struct GraphNode* temp = current;
            current = current->next;
            free(temp);
        }
    }
    free(graph->adjacencyList);
    free(graph->inDegree);
    free(graph);
}
int main() {
    char* words[] = {"wrt", "wrf", "er", "ett", "rftt"};
    int n = sizeof(words) / sizeof(words[0]);
    alienDictionary(words, n);
    return 0;
}

Output:

In summary, the Alien Dictionary Problem is an intriguing puzzle that assesses our knowledge of data structures and algorithms and has real-world applications in a variety of industries. Its variations and answers demonstrate how versatile computational problem-solving is, as well as how well it can handle intricate linguistic puzzles.

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