LeetCode-139. Word Break [C++][Java]

LeetCode-139. Word Breakhttps://leetcode.com/problems/word-break/

题目描述

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.

Note that the same word in the dictionary may be reused multiple times in the segmentation.

Example 1:

Input: s = "leetcode", wordDict = ["leet","code"]
Output: true
Explanation: Return true because "leetcode" can be segmented as "leet code".

Example 2:

Input: s = "applepenapple", wordDict = ["apple","pen"]
Output: true
Explanation: Return true because "applepenapple" can be segmented as "apple pen apple".
Note that you are allowed to reuse a dictionary word.

Example 3:

Input: s = "catsandog", wordDict = ["cats","dog","sand","and","cat"]
Output: false

Constraints:

• 1 <= s.length <= 300
• 1 <= wordDict.length <= 1000
• 1 <= wordDict[i].length <= 20
• s and wordDict[i] consist of only lowercase English letters.
• All the strings of wordDict are unique.

解题思路

【C++】

class Solution {
public:
    bool wordBreak(string s, vector& wordDict) {
        int n = s.length();
        vector dp(n + 1, false);
        dp[0] = true;
        for (int i = 1; i <= n; ++i) {
            for (const string & word : wordDict) {
                int len = word.length();
                if (i >= len && s.substr(i-len, len) == word) {
                    dp[i] = dp[i] || dp[i-len];
                }
            }
        }
        return dp[n];
    }
};

【Java】

class Solution {
    public boolean wordBreak(String s, List wordDict) {
        int n = s.length();
        boolean[] dp = new boolean[n + 1];
        dp[0] = true;
        for (int i = 1; i <= n; ++i) {
            for (String word : wordDict) {
                int len = word.length();
                if (i >= len && s.substring(i-len, i).equals(word)) {
                    dp[i] = dp[i] || dp[i-len];
                }
            }
        }
        return dp[n];
    }
}

参考文献

【1】java：String使用equals和==比较的区别_越来越好ing的博客-CSDN博客_java字符串比较