# [LeetCode 150] Evaluate Reverse Polish Notation

### Question

link

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are `+`, `-`, `*`, `/`. Each operand may be an integer or another expression.

Some examples:

```  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
```

### Stats

 Adjusted Difficulty 2 Time to use --------

Ratings/Color = 1(white) 2(lime) 3(yellow) 4/5(red)

### Analysis

This is a classic question. It’s easy.

### Code

my code

``````public int evalRPN(String[] tokens) {
if (tokens == null || tokens.length == 0)
return 0;
Stack<Integer> stack = new Stack<Integer>();
for (int p = 0; p < tokens.length; p ++) {
char cur = tokens[p].charAt(0);
if (cur >= '0' && cur <= '9'
|| tokens[p].length() > 1)
stack.push(Integer.parseInt(tokens[p]));
else if (cur == '+') {
int num1 = stack.pop();
int num2 = stack.pop();
stack.push(num1 + num2);
}
else if (cur == '-') {
int num1 = stack.pop();
int num2 = stack.pop();
stack.push(num2 - num1);
}
else if (cur == '*') {
int num1 = stack.pop();
int num2 = stack.pop();
stack.push(num1 * num2);
}
else if (cur == '/') {
int num1 = stack.pop();
int num2 = stack.pop();
stack.push(num2 / num1);
}
}
return stack.pop();
}
``````