剑指Offer的学习笔记（C#篇）-- 替换空格

class Solution
{
    public string replaceSpace(string str)
    {
        return str.Replace(" ","%20");
    }
}

public static void ReplaceBlank(char[] target, int maxLength)
    {
        if (target == null || maxLength <= 0)
        {
            return;
        }

        // originalLength 为字符串target的实际长度
        int originalLength = 0;
        int blankCount = 0;
        int i = 0;

        while (target[i] != '\0')
        {
            originalLength++;
            // 计算空格数量
            if (target[i] == ' ')
            {
                blankCount++;
            }
            i++;
        }

        // newLength 为把空格替换成'%20'之后的长度
        int newLength = originalLength + 2 * blankCount;
        if (newLength > maxLength)
        {
            return;
        }

        // 设置两个指针，一个指向原始字符串的末尾，另一个指向替换之后的字符串的末尾
        int indexOfOriginal = originalLength;
        int indexOfNew = newLength;

        while (indexOfOriginal >= 0 && indexOfNew >= 0)
        {
            if (target[indexOfOriginal] == ' ')
            {
                target[indexOfNew--] = '0';
                target[indexOfNew--] = '2';
                target[indexOfNew--] = '%';
            }
            else
            {
                target[indexOfNew--] = target[indexOfOriginal];
            }

            indexOfOriginal--;
        }
    }