class Solution {

public:

int calculate(string s)

{

string S = "+";

for (auto ch:s)

{

if (ch==' ') continue;

S+=ch;

if (ch=='(')

S+="+";

}

s = S;

stack<int>nums;

stack<int>signs;

int sum = 0, sign;

for (int i=0; i<s.size(); i++)

{

if (s[i]=='+'||s[i]=='-')

{

sign = s[i]=='+'?1:-1;

}

else if (isdigit(s[i]))

{

int j = i;

while (j<s.size() && isdigit(s[j]))

j++;

int num = stoi(s.substr(i,j-i));

i = j-1;

sum += num*sign;

}

else if (s[i]=='(')

{

nums.push(sum);

signs.push(sign);

sum = 0;

}

else if (s[i]==')')

{

sum = nums.top() + signs.top() * sum;

nums.pop();

signs.pop();

}

}

return sum;

}

};