Classic example
Input
board = [['o','a','a','n'],['e','t','a','e'],['i','h','k','r'],['i','f','l','v']]; words = ['oath','pea','eat','rain']
Output
['eat', 'oath']
'oath' and 'eat' can be constructed; 'pea' and 'rain' cannot. Output is sorted.
Full lesson preview
Find multiple words in a grid
Search a grid for multiple given words using backtracking; return which words exist.
Python practice32 minRecursion & BacktrackingAdvancedLast updated March 27, 2026
Problem statement
Given an m x n board of characters and a list of words, return all words that can be found in the board. A word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same cell may not be used more than once in a single word. Return the found words as a list sorted lexicographically and do not include duplicates even if a word can be formed multiple ways.
Task
Implement a search that finds which words from a list are present in a board by connecting adjacent cells (up/down/left/right) without reusing a cell in a single word search.
Examples
Input format
Two arguments: board — list of lists of single-character strings; words — list of strings.
Output format
List of found words sorted lexicographically (unique).
Constraints
1 <= m, n <= 6; words length small for brute-force backtracking. You may assume letters are lowercase.
Samples
Sample 1
Input
board = [['a','b'],['c','d']]; words = ['abcb']
Output
[]
Although 'abc' is adjacent, 'abcb' would require revisiting a cell which isn't allowed.