String to Number转换中的性能问题 [英] Performance issue in String to Number conversion

问题描述

我有空格分隔的字符串，其间包含数字：

I have space separated string containing numbers in between like:

abc123 ws32wd3 y3tg43 5tga89 a1a

我必须解析字符串以获取每个标记的数字，然后总结从标记中提取的所有数字。我写了下面的代码，但我认为，如果有大字符串，那么可能存在性能问题。

I have to parse the string to get the numbers from each token and then sum up all the digits extracted from tokens. I have written below code, but what I think is, if there is huge string, then there might be performance issue.

所以，我的问题是：

1. 我们如何改善以下代码中的表现？

1. How can we improve the performance in below code?

我们是否有其他方法可以编写以下代码来解决问题？

Do we have another way to write the below code to solve the problem?

代码：

public class TestSum {

    public static int doSum(String str){
        String[] sArray = str.split(" ");
        char[] chr = null;
        String temp;
        String number = "";
        int sum=0;
        for(String s : sArray){
            chr = s.toCharArray();
            for(char c : chr){
                temp = String.valueOf(c);
                if(isNum(temp)){
                    number = number + temp;
                }           
            }
            sum = sum + Integer.parseInt(number);
            number="";
        }       
        return sum;
    }

    public static boolean isNum(String nStr){   
        try{
            Integer.parseInt(nStr);
            return true;
        }catch(NumberFormatException nfe){
            return false;
        }       
    }

    public static void main(String[] args) {
        System.out.println("Sum is "+ TestSum.doSum("abc123 ws32wd3 y3tg43 5tga89 a1a"));
    }
} 

推荐答案

这是我能想到的最快的：

This is the fastest I could think of:

public static int getSum(String str) 
{
    int sum = 0;
    int exp = 1;      
    for (int i = str.length() - 1; i >= 0; i--) 
    {
        final char c = str.charAt(i);
        if (c >= '0' && c <= '9')
        {
            sum += (c - '0') * exp;
            exp *= 10;
        }
        else
        {
            exp = 1;
        }
    }
    return sum;
}

它从右到左迭代字符串。多亏了这一点，当它看到一个数字时，它可以添加适当的值，具体取决于数字中看到的小数位。

It iterates through string from right to left. Thanks to that, when it "sees" a digit it can add appropriate value, depending on the decimal position "seen" in the number.

结果与 davecom的基准测试：

AUTHOR       RUNTIME (NS)   HOW MANY TIMES FASTER THAN JUNS
-----------------------------------------------------------
Adam              66.221                                600
Old              579.873                                 70
Prabhakaran   20,012.750                                  2 (2x faster than Juns)
Juns          39,681.074                                  1

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