179. Largest Number

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.
转载于此
思路：确定两个字符串的先后顺序，如s1=”91”,s2=”9”,它就两种组合方式：s1+s2=”919”及s2+s1=”991”，因为”991”比较大，所以s2在前。然后，整个字符串数组都按照这种方法排列好。

string largestNumber(vector<int>& nums) {       vector<string> numstr;       for(auto it:nums)       numstr.push_back(to_string(it));       sort(numstr.begin(),numstr.end(),[](string& s1,string &s2){return s1+s2>s2+s1;});       string r;       for(auto str:numstr)        r+=str;        if(r[0]=='0'&&r.size()>0)        r='0';        return r;    }

这里排序的时间复杂度是O(nlgn),n是数组长度。空间复杂度：O(m)，m是最后结果字符串的长度。