Word Break

Description

Given a string s and a dictionary of words dict, determine if s can be break into a space-separated sequence of one or more dictionary words.

Example
Given s = "lintcode", dict = ["lint", "code"].
Return true because "lintcode" can be break as "lint code".

Link

Lintcode_ladder

Method

1. Dp, record reaching current char we can find valid break
2. x

Example

1. 1

class Solution {
public:
    /**
     * @param s: A string s
     * @param dict: A dictionary of words dict
     */
    bool wordBreak(string s, unordered_set<string> &wordDict) {
        // write your code here
        // if (s.empty() || wordDict.empty()) {
        //     return false;
        // }
        // optimizing 
        int longestw = 0;
        for (string i : wordDict) {
            longestw = max(longestw, (int)i.size());
        }
        int n = s.size();
        vector<bool> dp(n+1, false);
        dp[0] = true;
        for (int i = 1; i <= n; ++i) {
            for (int j =i-1; j >= max(i-longestw, 0); --j) {
                if (dp[j]) {
                    // int start = j;
                    // int count = i-j;
                    string tmp = s.substr(j, i-j);
                    // if we are surely to find "true" for dp[i], can jump out of inner for
                    if (wordDict.find(tmp) != wordDict.end()) {
                        dp[i] = true;
                        break; 
                    }
                }
            }
        }
        return dp[n];
    }
};

Similar problems

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Tags

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