290. Word Pattern

最新推荐文章于 2024-03-05 15:25:25 发布

原创最新推荐文章于 2024-03-05 15:25:25 发布 · 338 阅读

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文章标签：

#hash #双向映射 #长度相等

本文介绍了一种基于哈希表实现的模式匹配算法，该算法能够判断给定的字符串是否遵循指定的模式。通过双向映射确保模式与字符串间存在一一对应的关系，并详细解释了其实现思路及代码细节。

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Given a pattern and a string str, find if str follows the same pattern.

Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str.

Examples:
pattern = “abba”, str = “dog cat cat dog” should return true.
pattern = “abba”, str = “dog cat cat fish” should return false.
pattern = “aaaa”, str = “dog cat cat dog” should return false.
pattern = “abba”, str = “dog dog dog dog” should return false.
Notes:
You may assume pattern contains only lowercase letters, and str contains lowercase letters separated by a single space.

s思路:
1. 由于是一一映射，所以需要两个hash分别负责从pattern->str，str->pattern的映射
2. 另外需要take care of the length consistence. In other words, the two should have the same length.

//方法１：hash
class Solution {
public:
    bool wordPattern(string pattern, string str) {
        //
        int n=str.size();
        unordered_map<string,string> mm1,mm2;
        int count=0;
        for(int i=0;i<str.size();i++){
            if(count>=n) return false;

            if(str[i]==' '){
                count++;
                continue;
            }
            int j=i;

            while(j<str.size()&&str[j]!=' '){
                j++;    
            }   
            string cur=str.substr(i,j-i);
            string p=pattern.substr(count,1);
            if(mm1.count(cur)&&mm2.count(p)){
                if(mm1[cur]!=p&&mm2[p]!=cur) return false;
            }else if((mm1.count(cur)==0)&&(mm2.count(p)==0)){
                mm1[cur]=p;
                mm2[p]=cur; 
            }else
                return false;
            i=j-1;

        }
        return count==pattern.size()-1;
    }
};