290. Word Pattern

问题描述

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.

题目链接：

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思路分析

判断一个由多个单词组成的string是否是和字母的出现顺序是相同的。

使用两个map，将字符和单词转换为int值，看是否匹配。最后对比word和char的数量是否一致。注意要将循环匹配值规定为一致。

代码

class Solution {
public:
    bool wordPattern(string pattern, string str) {
        map<char, int> p2i;
        map<string, int> w2i;
        istringstream in(str);
        int i = 0, n = pattern.length();
        for(string word; in >> word; i++){
            if (p2i[pattern[i]] != w2i[word])
                return false;
            p2i[pattern[i]] = w2i[word] = i + 1;
        }
        return i==n;
    }
};

时间复杂度：$O(n)$
空间复杂度：$O(n)$

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反思

对于hash table的应用。还有iostream，已经有些陌生了。