word search problem

The word search problem is a classic problem in computer science and involves searching for a given word in a two-dimensional grid of characters. In this problem, we are given a grid of characters and a target word, and we need to find if the word exists in the grid. The word can be constructed by starting from any cell in the grid and moving in any of the four directions (up, down, left, or right) to create a chain of adjacent cells. Each cell can only be used once, and the word must be formed using only the cells visited in the correct order.

One of the most common approaches to solving this problem is to use depth-first search (DFS). The idea is to start at each cell in the grid and recursively search for the next character in the target word in each of the neighboring cells. We maintain a visited set to keep track of the cells we have already visited, and we mark each cell as visited as we traverse it. If we find the entire word, we return True, otherwise, we backtrack and mark the current cell as unvisited and try another direction.

understanding word search using example of game player :

Word search is a game where a player tries to find words hidden in a grid of letters. The words can be arranged horizontally, vertically, or diagonally and can be spelled forwards or backwards. Depth-First Search (DFS) is an algorithm that can be used to solve word search puzzles.

Here’s an example of how DFS can be used to solve a word search puzzle:

Suppose we have the following grid of letters:

S L R E
I T O N
G N I K
N I W O

And we want to find the word “STRING”. We can use DFS to search for the word as follows:

1. We start by scanning the grid for the first letter of the word “S”. We find it in the top left corner.
2. We mark the “S” as visited and check its neighboring cells to see if any of them contain the next letter of the word “T”.
3. We find the “T” to the right of the “S”, so we mark it as visited and continue the search for the next letter.
4. We search for the next letter “R” by checking the neighboring cells of the “T”. We find the “R” below the “T”, so we mark it as visited and continue the search.
5. We continue to search for the next letters “I”, “N”, and “G” in the same way, marking each letter as visited and checking its neighboring cells for the next letter in the word.
6. Finally, we find the last letter “G” in the bottom right corner of the grid, and we have successfully found the word “STRING”.

source code:https://leetcode.com/problems/word-search/description/

Let’s take a look at the code provided to understand this algorithm better. The exist method takes in the grid and the target word and returns True if the word exists in the grid and False otherwise. It does this by iterating over every cell in the grid and calling the solve method for each cell that matches the first character of the target word. It also initializes a visited dictionary to keep track of the cells we have already visited.

The solve method takes in the current cell, the current index in the target word, and the visited set. It first checks if we have found the entire word by comparing the current index with the length of the target word. If we have found the entire word, we set the res list to True and return. Otherwise, we iterate over each neighboring cell and check if it matches the next character in the target word and has not been visited before. If it satisfies these conditions, we mark it as visited and recursively call the solve method for the next character in the target word. If we find the entire word in this way, we set res to True and return. Otherwise, we mark the current cell as unvisited and try another direction.