（未AC）7-4 求指定层的元素个数 (25分)

[1,2,[3,4,[5,6],7],8]
3

2

 1 #include<iostream>
 2 #include<stack>
 3 #include<string>
 4 #include<cctype>
 5 using namespace std;
 6 int main()
 7 {
 8     stack<int>stk;
 9     string s;
10     int N, sum = 0, k = 0;
11     cin >> s;
12     cin >> N;
13     for (int i = 0; i < s.length(); i++)
14     {
15         if (isalnum(s[i])||s[i]==‘[‘)
16         {
17             if (s[i] == ‘[‘)
18                 sum++;
19             stk.push(s[i]);
20         }
21         if (s[i]==‘]‘)
22         {
23             while (stk.top()!=‘[‘)
24             {
25             stk.pop();
26             k++;
27             }
28             stk.pop();
29         if (N==sum)
30         {
31             cout << k;
32             break;
33         }
34         else
35         {
36             k = 0;
37         }
38         sum--;
39         }
40     }
41 }