題目描述(Medium)

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

Note:

• The same word in the dictionary may be reused multiple times in the segmentation.
• You may assume the dictionary does not contain duplicate words.

題目連結

https://leetcode.com/problems/word-break/description/

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

演算法分析

設狀態為f(i)，表示s[0,i]是否可以分詞，則狀態轉移方程為

提交程式碼：

class Solution {
public:
    bool wordBreak(string s, vector<string>& wordDict) {
        const int n = s.size();
        vector<bool> f(n + 1, false);
        f[0] = true;
        
        for (int i = 1; i <= n; ++i) {
            for (int j = i - 1; j >= 0; --j) {
                
                if (f[j] && find(wordDict.begin(), wordDict.end(), 
                                 s.substr(j, i - j)) != wordDict.end()) {
                    f[i] = true;
                    break;
                }
            }
        }
        
        return f[n];
    }
};