报错说没有匹配的min（），但是把参数单独定义一下又没问题了，这是为什么？

Question

用下列代码解决541. 反转字符串 II

string reverseStr(string s, int k) {
    for(int i=0;i<s.size();i+=2*k){
        reverse(s.begin()+i,s.begin()+min(i+k,s.size()));
    }
    return s;
}

报错说找不到min()方法：

Line 5: Char 43: error: no matching function for call to 'min'
            reverse(s.begin()+i,s.begin()+min(i+k,s.size()));
                                          ^~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/algorithmfwd.h:383:5: note: candidate template ignored: deduced conflicting types for parameter '_Tp' ('int' vs. 'unsigned long')
    min(const _Tp&, const _Tp&);
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_algo.h:3450:5: note: candidate template ignored: could not match 'initializer_list<type-parameter-0-0>' against 'int'
    min(initializer_list<_Tp> __l, _Compare __comp)
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_algo.h:3444:5: note: candidate function template not viable: requires single argument '__l', but 2 arguments were provided
    min(initializer_list<_Tp> __l)
    ^
/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/algorithmfwd.h:388:5: note: candidate function template not viable: requires 3 arguments, but 2 were provided
    min(const _Tp&, const _Tp&, _Compare);
    ^
1 error generated.

但是把s.size()单独dia出来定义一个参数就好了。

string reverseStr(string s, int k) {
    int n=s.size();
    for(int i=0;i<s.size();i+=2*k){
        reverse(s.begin()+i,s.begin()+min(i+k,n));
    }
    return s;
}

这是为什么？

Answer 1

min比较的类型要一致
min(i+k,s.size())) --> i +k 为int, s.size()为unsigned long
改成下面这种
min(i+k,n) -->类型匹配了，就没问题