字符串作为映射中的键，自定义比较功能

Question

我在地图中使用字符串作为键值并尝试自定义比较函数。当我通过比较字符串的长度来自定义比较函数时，映射无法区分具有相同大小的不同字符串。代码如下：

class Solution {
public:
int findLUSlength(vector<string>& strs) {
    if(strs.size() < 2) return -1;
    auto cmpByStringLength = [](const string &s1, const string &s2)->bool
                        {
                            return s1.size() < s2.size();
                        };
    map<string, int, decltype(cmpByStringLength)> mpstringcount(cmpByStringLength);
    for(int i = 0; i < strs.size(); i++)
        mpstringcount[strs[i]]++;
    for(auto itmp = mpstringcount.begin(); itmp != mpstringcount.end(); itmp++)
    {
        cout << "itmp->first: " << itmp->first << endl;
    }
    return -1;
}
};

如果我输入的字符串是["aba","cdc","eae","abcd"]，代码只会输出："abcd"和"aba"。

Answer 1

the map fail to tell the different strings with same size.

请注意，提供给 std::map 的比较器不仅用于排序，还用于相等性检查。

Everywhere the standard library uses the Compare concept, uniqueness is determined by using the equivalence relation. In imprecise terms, two objects a and b are considered equivalent (not unique) if neither compares less than the other: !comp(a, b) && !comp(b, a).

和std::map存储具有唯一键的元素。您的比较函子根据长度比较 strings，然后对于这些具有相同长度的 strings 将只存储其中一个。从一个map<string, int, decltype(cmpByStringLength)>、"aba"、"cdc"、"eae"的角度来看，都是一样的string。

字符串作为映射中的键，自定义比较功能

string as key in map, custom the compare function

c++

stdmap

stdstring

comparator

c++11