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224. Basic Calculator - stack.cpp
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224. Basic Calculator - stack.cpp
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class Solution {
public:
int calculate(string s) {
int res = 0, num = 0, first, second;
char op;
vector<int> operands;
vector<char> operators;
for(int i = 0; i <= s.length(); ++i){
if(i == s.length() || s[i] == ')' || s[i] == '+' || s[i] == '-'){
while(!operators.empty() && (i == s.length() || operators.back() != '(')){
op = operators.back(), operators.pop_back();
second = operands.back(), operands.pop_back();
first = operands.back(), operands.pop_back();
operands.push_back(op == '+' ? first + second : first - second);
}
if(i == s.length()) break;
else if(s[i] == ')')
operators.pop_back();
else
operators.push_back(s[i]);
}
else if(s[i] == ' ') continue;
else if(s[i] == '(')
operators.push_back(s[i]);
else{
num = 0;
while(isdigit(s[i]))
num = num * 10 + s[i++] - '0';
operands.push_back(num);
i--;
}
}
return operands.back();
}
};