Reorder array to construct the minimum number

Construct minimum number by reordering a given non-negative integer array. Arrange them such that they form the minimum number.

Notice

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

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Example

Given [3, 32, 321], there are 6 possible numbers can be constructed by reordering the array:

3+32+321=332321
3+321+32=332132
32+3+321=323321
32+321+3=323213
321+3+32=321332
321+32+3=321323

So after reordering, the minimum number is 321323, and return it.

分析：

这里需要对数组进行排序，那么怎么比较大小呢？对于数A和B，如果AB在一起组成的数小于BA组成的数，我们就认为A<B,反之亦然。

public static String minNumber(int[] nums) {
    if (nums == null || nums.length == 0)
        return "";

    String[] strs = new String[nums.length];
    for (int i = 0; i < nums.length; i++) {
        strs[i] = String.valueOf(nums[i]);
    }

    Arrays.sort(strs, new Comparator<String>() {
        public int compare(String str1, String str2) {
            return (str1 + str2).compareTo(str2 + str1);
        }
    });

    StringBuilder sb = new StringBuilder();
    for (String str : strs) {
        sb.append(str);
    }
    for (int i = 0; i < sb.length(); i++) {
        if (sb.charAt(i) != '0') {
            return sb.substring(i);
        }
    }
    return "0";
}