字符串重新排列，让里面不能有相同字母在一起。比如aaabbb非法的，要让它变成ababab。给一种即可

 package ReorderString;

 import java.util.*;

 public class Solution {

     class Element {

         char val;

         int appear;

         public Element(char value) {

             this.val = value;

             this.appear = 1;

         }

     }

     public String reorder(String str) {

         Element[] summary = new Element[26];

         for (int i=0; i<str.length(); i++) {

             char cur = str.charAt(i);

             if (summary[(int)(cur-'a')] == null) {

                 summary[(int)(cur-'a')] = new Element(cur);

             }

             else {

                 summary[(int)(cur-'a')].appear++;

             }

         }

         PriorityQueue<Element> queue = new PriorityQueue<Element>(11, new Comparator<Element>() {

             public int compare(Element e1, Element e2) {

                 return e2.appear - e1.appear;

             }

         });

         for (Element each : summary) {

             if (each != null) {

                 queue.offer(each);

             }

         }

         Queue<Element> store = new LinkedList<Element>();

         StringBuffer res = new StringBuffer();

         while (!queue.isEmpty() || !store.isEmpty()) {

             if (!queue.isEmpty()) {

                 Element cur = queue.poll();

                 if (res.length()==0 || cur.val!=res.charAt(res.length()-1)) {

                     res.append(cur.val);

                     cur.appear--;

                     if (cur.appear > 0) store.offer(cur);

                     while (!store.isEmpty()) {

                         queue.offer(store.poll());

                     }

                 }

                 else { //cur.val equals last char in res

                     store.offer(cur);

                 }

             }

             else { //store is not empty but queue is empty

                 res = new StringBuffer();

                 res.append(-1);

                 return res.toString();

             }

         }

         return res.toString();

     }

     /**

      * @param args

      */

     public static void main(String[] args) {

         // TODO Auto-generated method stub

         Solution sol = new Solution();

         String res = sol.reorder("aaabbba");

         System.out.println(res);

     }

 }