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飞过闲红千叶，夕岸在哪
类目归类
[LeetCode 150] Evaluate Reverse Polish Notation [Java]
12/22
1. Description
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
2. Example
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
3. Code
import java.util.Stack;
public class LeetCode0150 {
public int evalRPN(String[] tokens) {
if(tokens == null || tokens.length == 0) {
return 0;
}
Stack stack = new Stack();
for(int i = 0; i< tokens.length; i++) {
String str = tokens[i];
if(str == " ") {
continue;
}
switch(str) {
case "+":
stack.push(stack.pop() + stack.pop());
break;
case "-":
int meiosis = stack.pop();
stack.push(stack.pop() - meiosis);
break;
case "*":
stack.push(stack.pop() * stack.pop());
break;
case "/":
int divisor = stack.pop();
stack.push(stack.pop() / divisor);
break;
default:
stack.push(Integer.parseInt(str));
}
}
return stack.pop();
}
public static void main(String[] args) {
LeetCode0150 leetcode = new LeetCode0150();
String[] tokens = new String[] {"4", "13", "5", "/", "+"};
System.out.println(leetcode.evalRPN(tokens));
}
}
