Basic Calculator II
Implement a basic calculator to evaluate a simple expression string.
The expression string contains only non-negative integers,
The expression string contains only non-negative integers,
+,-,*,/ operators and empty spaces . The integer division should truncate toward zero.
You may assume that the given expression is always valid.
Some examples:
"3+2*2" = 7
" 3/2 " = 1
" 3+5 / 2 " = 5
：
1. ， 44 - op op == '+' ? 1 : -1。また、>>スペースをスキップできます
int calculate(string s) {
istringstream in('+' + s + '+');
long long total = 0, term = 0, n;
char op;
while (in >> op) {
if (op == '+' or op == '-') {
total += term;
in >> term;
term *= 44 - op;
} else {
in >> n;
if (op == '*')
term *= n;
else
term /= n;
}
}
return total;
}
2.わかりやすく、 する い でもあります. の の れたコードでもありますint calculate(string s) {
int result = 0, cur_res = 0;
char op = '+';
for(int pos = s.find_first_not_of(' '); pos < s.size(); pos = s.find_first_not_of(' ', pos)) {
if(isdigit(s[pos])) {
int tmp = s[pos] - '0';
while(++pos < s.size() && isdigit(s[pos]))
tmp = tmp*10 + (s[pos] - '0');
switch(op) {
case '+' : cur_res += tmp; break;
case '-' : cur_res -= tmp; break;
case '*' : cur_res *= tmp; break;
case '/' : cur_res /= tmp; break;
}
}
else {
if(s[pos] == '+' || s[pos] == '-') {
result += cur_res;
cur_res = 0;
}
op = s[pos++];
}
}
return result + cur_res;
}
3.このスタックを うのも な ですint calculate(string s) {
stack<int> myStack;
char sign = '+';
int res = 0, tmp = 0;
for (unsigned int i = 0; i < s.size(); i++) {
if (isdigit(s[i]))
tmp = 10*tmp + s[i]-'0';
if (!isdigit(s[i]) && !isspace(s[i]) || i == s.size()-1) {
if (sign == '-')
myStack.push(-tmp);
else if (sign == '+')
myStack.push(tmp);
else {
int num;
if (sign == '*' )
num = myStack.top()*tmp;
else
num = myStack.top()/tmp;
myStack.pop();
myStack.push(num);
}
sign = s[i];
tmp = 0;
}
}
while (!myStack.empty()) {
res += myStack.top();
myStack.pop();
}
return res;
}