# 面试题 16.18

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## 面试题 16.18

难度:Medium

> 你有两个字符串，即pattern和value。 pattern字符串由字母"a"和"b"组成，用于描述字符串中的模式。例如，字符串"catcatgocatgo"匹配模式"aabab"（其中"cat"是"a"，"go"是"b"），该字符串也匹配像"a"、"ab"和"b"这样的模式。但需注意"a"和"b"不能同时表示相同的字符串。编写一个方法判断value字符串是否匹配pattern字符串。

````
```
示例 1：

输入： pattern = "abba", value = "dogcatcatdog"
输出： true
示例 2：

输入： pattern = "abba", value = "dogcatcatfish"
输出： false
示例 3：

输入： pattern = "aaaa", value = "dogcatcatdog"
输出： false
示例 4：

输入： pattern = "abba", value = "dogdogdogdog"
输出： true
解释： "a"="dogdog",b=""，反之也符合规则
提示：

0 <= len(pattern) <= 1000
0 <= len(value) <= 1000
你可以假设pattern只包含字母"a"和"b"，value仅包含小写字母。
```
````

可以通过一个二元一次方程来逐个判断每个pattern出现的次数，即numA*lenA+numB*lenB=lenValue;

````
```
class Solution {
string pattern;
inline string patternString(string a, string b)
{
    string res;
    for(auto c: pattern)
    {
	if(c=='a') res+=a;
	else res+=b;
    }
    return res;
}
public:
bool patternMatching(string pattern, string value) {

    int sizeA=0;
    int sizeB=0;

    if(pattern[0]=='b') 
    {
	string tmp;
	for(auto c:pattern)
	    tmp+= c=='a' ? 'b' :'a';
	this->pattern=tmp;
    }
    else 
	this->pattern=pattern;

    for(auto c:this->pattern)
    {
	if(c=='a') sizeA++;
	else sizeB++;
    }

    if(sizeA ==0 && sizeB ==0) return value=="";
    if(sizeA==0) 
    {
	int cntB=value.length()/sizeB;
	return patternString("",value.substr(0,cntB)) ==value;
    }
    if(sizeB==0) 
    {
	int cntA=value.length()/sizeA;
	return patternString(value.substr(0,cntA),"") ==value;
    }
    int startB=0;
    for(auto c:this->pattern)
    {
	if(c=='a') {
	    startB++;
	}
	else 
	    break;
    }
    //cout<<startB<<endl;
    //cout<<sizeA<<endl;
    int cntA=value.length()/sizeA;
    //     cout<<cntA<<endl;
    for(int i=0; i<=cntA;i++)
    {
	int cntB=(value.length()-sizeA*i)/sizeB;

	string a=value.substr(0,i);
	//      cout<<i*startB<<endl;
	string b =value.substr(i*startB,cntB);
	//       cout<<a<<"  "<<b<<endl;
	if(a==b) continue;
	//    cout<<patternString(a,b) <<endl;
	if(patternString(a,b) == value) return true;

    }
    return false;
}
};
````

```
> 执行用时 :4 ms, 在所有 C++ 提交中击败了63.82%的用户   
内存消耗 :10.1 MB, 在所有 C++ 提交中击败了100.00%的用户
```


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