# 1079.Letter Tile Possibilities

**1079.Letter Tile Possibilities**

难度:Medium

> 你有一套活字字模 tiles，其中每个字模上都刻有一个字母 tiles\[i]。返回你可以印出的非空字母序列的数目。

```
示例 1：

输入："AAB"
输出：8
解释：可能的序列为 "A", "B", "AA", "AB", "BA", "AAB", "ABA", "BAA"。
示例 2：

输入："AAABBC"
输出：188
 

提示：

1 <= tiles.length <= 7
tiles 由大写英文字母组成
```

树形结构，递归求解，首先需要确定不同的字符数，可以使用map来统计，递归终止条件，是某个字符出现次数为0，此时到达叶子节点，统计整个数的节点数目即为所求。

```
class Solution {
int cnt=0;
void numTile(unordered_map<char, int> alpha)
{
    for(auto a:alpha)
    {
        if(a.second) 
        {
            cnt++;
            unordered_map<char, int>tmp(alpha);
            tmp[a.first]--;
            numTile(tmp);
        }
    }
}
public:
    int numTilePossibilities(string tiles) {
        unordered_map<char,int>alpha;
        for(auto t:tiles)
        alpha[t]++;
        numTile(alpha);
        return cnt;
    }
};
```

> 执行用时 :268 ms, 在所有 C++ 提交中击败了10.83%的用户\
> 内存消耗 :74.5 MB, 在所有 C++ 提交中击败了100.00%的用户


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