剑指offer（题四）

题意：将一个字符串中所有的空格替换成指定的字符串。
思路：先遍历字符串，计算有多少空格，再计算将该字符串中空格替换了指定字符串后，替换后的长度是多大。初始化一个长度为替换后长度的数组，设定两个游标，index1指向替换后数组的末尾，index2指向替换前字符串的末尾，从后往前遍历，若index2指定的字符为空格，则在index1指定的位置加上待替换的字符串，否则则将字符复制至index1位置。
代码：

package MianShiTi_4;

public class MianShiTi_4 {
    public static int countSpace(String newstring){
        int count =0;
        for(int i = 0; i< newstring.length() ; i++){
            if(newstring.charAt(i) == ' '){
                count++;
            }
        }
        return count;
    }

    public static int  calLength(String newstring) {
        int length = 0;
        int spaceCount = 0;
        spaceCount = countSpace(newstring);
        length = newstring.length() + spaceCount*2;
        return length;
    }

    public String replaceAllSpace(String newString){
        String s1;
        int newlength = calLength(newString);
        int originalLength = newString.length();
        char []tempArray = new char[newlength];
        System.arraycopy(newString.toCharArray(), 0, tempArray, 0, newString.toCharArray().length);
        int indexOfString = originalLength - 1;
        int indexOfNewString = newlength - 1;
        while (indexOfString >=0 && indexOfString != indexOfNewString) {
            if(newString.charAt(indexOfString) == ' '){
                tempArray[indexOfNewString--] = '0';
                tempArray[indexOfNewString--] = '2';
                tempArray[indexOfNewString--] = '%';
            }else{
                tempArray[indexOfNewString-- ] = tempArray[indexOfString];
            }
            indexOfString --;
        }
        s1 =new String(tempArray);
        return s1;
    }

    public static void main(String[] args) {
        String string = "I am ok";
        MianShiTi_4 test = new MianShiTi_4();
        int count1 = test.countSpace(string);
        int count2 = test.calLength(string);
        String s2;
        s2 = test.replaceAllSpace(string);
        System.out.println(s2);
        //System.out.println(count1+"   "+count2);
    }
}