最近做了幾套華為的機試題，今天有時間，把之前寫的幾套程式碼全都貼出來。題目都只記得個大概，將就著看吧，不過程式碼都是完整的，自認為寫的還行。

題目描述

大概意思是：實現一個加減乘的計算。給定的樣式是一個字串，且該字串為正確的字串；需要運算的數字均為正數，且每個數字前只有一個運算子。

Java程式碼

初始思路比較笨，對字串從左到右一個一個的做判斷。分割出數字和運算子號後，先算乘法，再算加減。寫完後回頭看程式碼，都有點鬱悶了，聽上去這麼簡單的功能，怎麼不小心，程式碼就這麼長了呢：

import java.util.Scanner;
import java.util.Stack;

public
 
 class Main2 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String line = scanner.nextLine();
        Stack<String> splitItems = getSplitItems(line);
        int res = getCalculationResult(splitItems);
        scanner.close();
        System.out.println(res);
    }

    public
 
 static Stack<String> getSplitItems(String line) {
        Stack<String> stackS = new Stack<String>();
        char[] charS = line.toCharArray();
        int accu = 0;
        boolean isNumReady = false;
        for(char c:charS) {
            if(c>='0' && c<='9') {
                accu = accu*10
 
 + (int)(c-'0');
                isNumReady = true;
            }else {
                if(isNumReady) {
                    stackS.add(String.valueOf(accu));
                }
                if(c=='+'||c=='-'||c=='*'){
                    stackS.add(String.valueOf(c));
                }else {
                    return null;
                }
                isNumReady = false;
                accu = 0;
            }
        }
        if(isNumReady) {
            stackS.add(String.valueOf(accu));
        }
        return stackS;
    }

    public static int getCalculationResult(Stack<String> stack) {
        if(stack==null) {
            return -1;
        }
        Stack<String> helpStack = new Stack<String>();
        while(!stack.isEmpty()) {
            String item = stack.pop();
            if(item.equals("*")) {
                int mult = Integer.parseInt(stack.pop()) * Integer.parseInt(helpStack.pop());
                helpStack.push(String.valueOf(mult));
            }else {
                helpStack.push(item);
            }
        }
        int resNum = Integer.valueOf(helpStack.pop());
        while(!helpStack.isEmpty()) {
            String s = helpStack.pop();
            if(s.equals("+")) {
                resNum += Integer.parseInt(helpStack.pop());
            }else if(s.equals("-")) {
                resNum -= Integer.parseInt(helpStack.pop());
            }
        }
        return resNum;
    }
}

剛突然靈光一閃，我為什麼不能用符號“+-*”來直接分隔出數字，用數字分隔出我需要的符號呢，這樣分別獲得儲存數字的棧和儲存符號的棧，計算起來豈不是更Easy？以下是我實現的程式碼：

import java.util.Scanner;
import java.util.Stack;

public class Main3 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String line = scanner.nextLine();
        Stack<Integer> splitNums = getSplitNums(line);
        Stack<String> splitStrs = getSplitStrs(line); 
        int res = getCalculationResult(splitNums, splitStrs);
        scanner.close();
        System.out.println(res);
    }

    public static Stack<Integer> getSplitNums(String line) {
        Stack<Integer> stackS = new Stack<>();
        String[] strArray = line.split("\\+|-|\\*");
        for(String s:strArray) {
            stackS.push(Integer.parseInt(s));
        }
        return stackS;
    }

    public static Stack<String> getSplitStrs(String line){
        Stack<String> stackS = new Stack<>();
        String[] strArray = line.split("[0-9]+");
        for(String s:strArray) {
            if(!s.equals("")){
                stackS.push(s);
            }
        }
        return stackS;
    }

    public static int getCalculationResult(Stack<Integer> nums, Stack<String> symbles) {
        Stack<Integer> numsStack = new Stack<>();
        Stack<String> symStack = new Stack<>();
        numsStack.push(nums.pop());
        while(!symbles.isEmpty()) {
            String symble = symbles.pop();
            if(symble.equals("*")) {
                numsStack.push(nums.pop() * numsStack.pop());
            }else {
                symStack.push(symble);
                numsStack.push(nums.pop());
            }
        }

        while(!symStack.isEmpty()) {
            int num = numsStack.pop();
            String symble = symStack.pop();
            if(symble.equals("+")){
                numsStack.push(num + numsStack.pop());
            }else if(symble.equals("-")) {
                numsStack.push(num - numsStack.pop());
            }
        }
        return numsStack.pop();
    }
}