LeetCode: Largest Number 解题报告 以及Comparator, CompareTo 应用

Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.

Note: The result may be very large, so you need to return a string instead of an integer.

Credits:

Special thanks to @ts for adding this problem and creating all test cases.

SOLUTION 1:

参考http://bookshadow.com/weblog/2015/01/13/leetcode-largest-number/的解法：

贪心思路：对于两个备选数字a和b，如果str(a) + str(b) > str(b) + str(a)，则a在b之前，否则b在a之前

按照此原则对原数组从大到小排序即可

时间复杂度O（nlogn）

易错样例：

Input:     [0,0]

Output:    "00"

Expected:  "0"

JAVA CODE:

 1 public class Solution {
 2     public String largestNumber(int[] num) {
 3         // 1045
 4         // 1111 begin.
 5         if (num == null) {
 6             return null;
 7         }
 8         
 9         ArrayList<Integer> list = new ArrayList<Integer>();
10         for (int n1: num) {
11             list.add(n1);
12         }
13         
14         Collections.sort(list, new Comparator<Integer>(){
15             public int compare(Integer o1, Integer o2) {
16                 String s1 = "" + o1 + o2;
17                 String s2 = "" + o2 + o1;
18                 
19                 return s2.compareTo(s1);
20             }
21         });
22         
23         StringBuilder sb = new StringBuilder();
24         for (int n: list) {
25             sb.append(n);
26         }
27         
28         if (sb.charAt(0) == '0') {
29             return "0";
30         }
31         
32         return sb.toString();
33     }
34 }

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