[LeetCode] Largest Number

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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.

这道题目一开始花了不少时间，思路也不好。把数字转换成字符串，方便不同长度的字符串从左往右逐个字符比较。但如果某一个字符串是另一个的前缀的话，即使把多余字符串和第一个字符比较，也还是遇到了不少情况要处理。

这题最简单的方法其实是，比较两个字符串s1和s2时，比较s1+s2和s2+s1即可。注意这里有一个特殊情况，就是组合后的字符串以0开始，需要把开始的0都去掉。

class StringComparator implements Comparator<String> {@Overridepublic int compare(String s1, String s2) {String s12 = s1 + s2;String s21 = s2 + s1;return (int) (Long.parseLong(s12) - Long.parseLong(s21));}}public String largestNumber(int[] num) {StringBuilder sb = new StringBuilder();List<String> numStr = new ArrayList<String>();for (int i : num)numStr.add("" + i);Collections.sort(numStr, new StringComparator());// Trim the leading zero(s).boolean HasPossibleLeading0 = true;for (int i = numStr.size() - 1; i >= 0; --i) {if (HasPossibleLeading0 && numStr.get(i).equals("0"))continue;HasPossibleLeading0 = false;sb.append(numStr.get(i));}if (sb.length() == 0) return "0";return sb.toString();}

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