java 给定一个算术表达式的字符串;其中只包含两个运算符：'+'，'*'，编写一个计算表达式的函数

Posted 2021-05-08

public class Solution {

	public static void main(String[] args) {
		String[] input = { "5", "4+20*3", "20*3+4", "20+20+20+4", "4*4*4" };
		for (String test : input)
			System.out.printf("%s = %d%n", test, eval(test));
	}

	private static int eval(String input) {
		int sum = 0;
		int multiplication = 1;
		String currentNumber = "";

		if (input.matches("\\d+"))
			return Integer.parseInt(input);

		for (int i = 0; i < input.length(); i++) {
			char currentChar = input.charAt(i);

			switch (currentChar) {
				case '+':
					sum += multiplication * Integer.parseInt(currentNumber);
					multiplication = 1;
					currentNumber = "";
					break;
	
				case '*':
					multiplication *= Integer.parseInt(currentNumber);
					currentNumber = "";
					break;
	
				default:
					currentNumber += currentChar;
					break;
			}
		}

		return sum += multiplication * Integer.parseInt(currentNumber);
	}
}