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Word Break II

Certification: Advanced Level Accuracy: 100% Submissions: 1 Points: 15

Write a Java program that given a string `s` and a dictionary of strings `wordDict`, returns all possible sentences that can be formed by breaking `s` into a sequence of one or more dictionary words, separated by spaces. The same word from the dictionary can be used multiple times. Return the sentences in any order.

Example 1
    
  
  • Input: s = "catsanddog", 
    wordDict = ["cat", "cats", "and", "sand", "dog"]
    • 
  
  • Output: ["cats and dog", "cat sand dog"]
    • 
  
  • Explanation: One possible breaking is "cats" + "and" + "dog" = "cats and dog". Another possible breaking is "cat" + "sand" + "dog" = "cat sand dog".
    •
Example 2
    
  
  • Input: s = "pineapplepenapple", 
    wordDict = ["apple", "pen", "applepen", "pine", "pineapple"]
    • 
  
  • Output: ["pine apple pen apple", "pineapple pen apple", "pine applepen apple"]
    • 
  
  • Explanation: There are three ways to break down "pineapplepenapple" into dictionary words.
    •
Constraints
    
  
  • 1 <= s.length <= 20
    • 
  
  • 1 <= wordDict.length <= 1000
    • 
  
  • 1 <= wordDict[i].length <= 10
    • 
  
  • s and wordDict[i] consist of only lowercase English letters
    • 
  
  • All strings in wordDict are unique
    • 
  
  • Time Complexity: O(2^n), where n is the length of the string s
    • 
  
  • Space Complexity: O(n * k), where k is the number of valid sentences
    •
StringsDynamic Programming Backtracking GoogleWalmart
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Hint
Solution

Solution Hints

    
  
  • Use a combination of backtracking and dynamic programming to solve this problem
    • 
  
  • Create a memoization map to store intermediate results, which can significantly improve performance
    • 
  
  • Use recursion to explore all possible ways to break the string
    • 
  
  • For each position in the string, check if there is a valid word in the dictionary that starts at that position
    • 
  
  • If a valid word is found, recursively process the remaining part of the string
    • 
  
  • Use a HashSet to quickly check if a word exists in the dictionary
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  • Build the sentences incrementally as you find valid word breaks
    •

Steps to solve by this approach:

 Step 1: Create a HashSet from the dictionary for constant-time word lookups.

 Step 2: Implement a memoization map to store previously computed results for substrings.

 Step 3: Use recursive backtracking to break down the problem into smaller subproblems.

 Step 4: For each position in the string, check if there's a valid word that starts at that position.

 Step 5: If a valid word is found, recursively process the remaining substring.

 Step 6: Combine the current word with all valid results from the remaining substring.

 Step 7: Store the computed results in the memoization map to avoid redundant calculations.

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