LeetCode Evaluate Reverse Polish Notation
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题目:
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答案,源代码:
public class Solution {
public int evalRPN(String[] tokens) {
HashMap<String, String> operaters = new HashMap<String, String>(){
{
put("+","");
put("/","");
put("-","");
put("*","");
}
};
Stack<Integer> params = new Stack<Integer>();
for (int i = 0; i < tokens.length; i++) {
if(operaters.containsKey(tokens[i])){
int num1=params.pop();
int num2=params.pop();
params.push(compite(num2, num1, tokens[i].charAt(0)));
}else{
params.push(Integer.parseInt(tokens[i]));
}
}
return params.pop();
}
public static int compite(int a, int b, char operators) {
int result = 0;
switch (operators) {
case '+':
result = a + b;
break;
case '-':
result = a - b;
break;
case '/':
result = a / b;
break;
case '*':
result = a * b;
break;
default:
System.out.println("operator error [" + operators + "]");
}
return result;
}
}
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