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【Java】大数相加
作者:PorcoGT / 发布于2015/5/19/ 556

	package algorithmProblem;
	
	
	/**
	* 大数处理
	* @author ronaldoGT
	*
	*/
	public class LargeNumber {
	
	 private static LargeNumber bigNum = new LargeNumber();
	
	 /**
	 * @param args
	 */
	 public static void main(String[] args) {
	 //加数
	 String addend = "199124184714717423989946727492472947629947662499747018091044924934153412170489450300035477372628428192873462348345625351232173";
	 //被加数
	 String augend = "9876655537290183759502716354829037465891039892732946122010234548910182881922526981973767374921010481924242565768827228398341849184889299292";
	 String str = bigNum.largeNumber(addend, augend);
	 System.out.println("number ="+bigNum.takeBack(str));
	 }
	
	 /**
	 * 大数相加
	 * 将超大数用字符串，然后反转操作字符串
	 * @param s1
	 * @param s2
	 * @return
	 */
	 public String largeNumber(String s1,String s2){
	 String min = s1.length() <= s2.length() ? s1:s2;
	 String max = s1.length() > s2.length() ? s1:s2;
	 int minSize = min.length();
	 int maxSize = max.length();
	 int index = 0;//标记是否发生进位
	 StringBuffer result = new StringBuffer();
	 for(int i = min.length()-1 ; i >= 0 ; i--) {//使用最小位数来进行循环,反向
	 int mark = Integer.parseInt(min.charAt(i) + "") + Integer.parseInt(max.charAt(i+(maxSize-minSize)) + "") + index;
	 if (mark >= 10) {
	 index = 1;
	 mark -= 10;
	 }else{
	 index = 0;
	 }
	 result.append(mark);
	 }
	 //当且仅当max,min位数一样时,并且发生进位
	 if(maxSize <= minSize){
	 if(index>0) {
	 result.append(index);
	 }
	 }else{
	 String highPosition = max.substring(0,maxSize-minSize);//截取max超出min的部分
	 if(highPosition.length()>9){//Integer是32位，范围-2147483648 到2147483648
	 //此处开始递归，确保每次送入的数都是正序排列的
	 result.append(largeNumber(highPosition, index + ""));
	 }else{
	 result.append(takeBack(Integer.parseInt(highPosition)+index+""));
	 }
	 }
	 return result.toString();
	 }
	
	 /**
	 * 反转字符串
	 * @param str
	 * @return
	 */
	 public String takeBack(String str){
	 StringBuffer result = new StringBuffer();
	 for(int i = str.length()-1 ; i >= 0 ; i--){
	 result.append(str.charAt(i));
	 }
	 return result.toString();
	 }
	}
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