MediumLeetCode #139Dynamic Programming

Word Break

Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words.

Constraints

1 <= s.length <= 300, 1 <= wordDict.length <= 1000

Examples

Input: s = "leetcode", wordDict = ["leet","code"]

Output: true

Solution

Approach

DP where dp[i] = true if s[0:i] can be segmented. For each position, check if any word in dict ends at that position and dp[i - len(word)] is true.

def wordBreak(s, wordDict):
    word_set = set(wordDict)
    dp = [False] * (len(s) + 1)
    dp[0] = True
    for i in range(1, len(s) + 1):
        for j in range(i):
            if dp[j] and s[j:i] in word_set:
                dp[i] = True
                break
    return dp[len(s)]

Complexity

Time:O(n² * m)

Space:O(n)

Hints

1.dp[i] = can we break s[0:i]?
2.Check all possible last words
3.Use set for O(1) word lookup

Asked at

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