替换空格

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剑指offer第四题，将空格替换为%20，一开始的实现

package com.zjy.sword2offer;public class SpaceReplace {public static String replace(String a){if(a==null||a.length()==0)return null;int count = 0;int originalLen = a.length();for(int i=0;i<originalLen;i++){if(a.charAt(i)==' ')count++;}int newLen = originalLen + count*2;int pOriginal = originalLen-1;int pNew = newLen-1;StringBuffer sb = new StringBuffer(newLen);while(pOriginal>=0 && pNew>pOriginal){if(a.charAt(pOriginal)!=' '){sb.insert(pNew--, a.charAt(pOriginal));}else{sb.insert(pNew-2, "%20");pNew -= 2;pNew--;}pOriginal--;}return sb.toString();}public static void main(String[] args) {// TODO Auto-generated method stubString str = "I am happy.";String res = replace(str);System.out.println(res);}}

一直报错如下

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsExceptionat java.lang.System.arraycopy(Native Method)at java.lang.AbstractStringBuilder.insert(Unknown Source)at java.lang.StringBuffer.insert(Unknown Source)at com.zjy.sword2offer.SpaceReplace.replace(SpaceReplace.java:27)at com.zjy.sword2offer.SpaceReplace.main(SpaceReplace.java:44)

猜想出错的原因在于StringBuffer初始化后内容是空的，不能直接从后边用setCharAt（）或者insert（）插入数据，否则报错，后来换了一个方式ok了，如下

package com.zjy.sword2offer;public class SpaceReplace {public static String replace(String a){if(a==null||a.length()==0)return null;int count = 0;int originalLen = a.length();for(int i=0;i<originalLen;i++){if(a.charAt(i)==' ')count++;}int newLen = originalLen + count*2;int pOriginal = originalLen-1;int pNew = newLen-1;StringBuffer sb = new StringBuffer(newLen);while(pOriginal>=0 && pNew>=0){char ch = a.charAt(pOriginal);if(ch!=' '){sb.append(ch);}else{sb.append("02%");}pOriginal--;}return sb.reverse().toString();}public static void main(String[] args) {// TODO Auto-generated method stubString str = "I am happy.";String res = replace(str);System.out.println(res);}}

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