179. Largest Number 排成最大的数字（重要！）

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https://leetcode.com/problems/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.

注意两点：

1.比较函数不是直接比较两个string的大小

因为30>3，但是3却因为放在前面；所以因为比较字符串组合起来的大小；

2.注意首位有0的情况

class Solution {public:struct cmp{bool operator()(const string& a, const string& b)const{string ab = a + b;string ba = b + a;return ab > ba;}//注意这个比较函数};string largestNumber(vector<int>& nums) {int len = nums.size();if (len == 0){return "";}vector<string> strNums(len);for (int i = 0; i < len; i++){strNums[i] = to_string(nums[i]);}sort(strNums.begin(), strNums.end(), cmp());string res;for (int i = 0; i < len; i++){res.append(strNums[i]);}//[0,0]的情况while (res.size()>1 && res[0]=='0'){res = res.substr(1);}return res;}};

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