/*

Company Tags : Airbnb

Leetcode Link : https://leetcode.com/problems/basic-calculator-ii/

*/

class Solution {

public:

int calculate(string s) {

int n = s.length();

int currNum = 0;

char prevOp = '+';

stack<int> st;

for(int i = 0; i<n; i++) {

if(isdigit(s[i])) {

currNum = currNum*10 + (s[i]-'0');

}

if(s[i] != ' ' && !isdigit(s[i]) || i == n-1) {

if(prevOp == '+') {

st.push(currNum);

} else if(prevOp == '-') {

st.push(-currNum);

} else if(prevOp == '/') {

int x = st.top();

st.pop();

st.push(x/currNum);

} else if(prevOp == '*') {

int x = st.top();

st.pop();

st.push(currNum*x);

}

currNum = 0;

prevOp = s[i];

}

}

int result = 0;

while(!st.empty()) {

result += st.top();

st.pop();

}

return result;

}

};