【LeetCode】290. Word Pattern

题目

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.

思路

最开始的思路是建立两个map，一个从char映射到string，一个从string映射到char。比较好的思路是保存一个相同的值，在这个题中就是出现的位置+1。+1的作用是避免0的干扰，因为map默认值就是0。

代码

class Solution {
public:
bool wordPattern(string pattern, string str) {
unordered_map<char,int> p2i;
unordered_map<string,int> s2i;
istringstream ss(str);
int i=0,n=pattern.size();
for (string word;ss>>word;++i){
if (i==n || p2i[pattern[i]]!=s2i[word]) return false;
p2i[pattern[i]]=s2i[word]=i+1;
}
return i==n;

}
};

字符串处理小技巧

此题中string中有空格，而c++中没有很方便的split函数，所以使用istringstream来处理string输入流。注意在平常使用时要包含头文件

include <sstream>

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