[LeetCode] Largest Number 排序

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.

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这题主要的需要考虑排序中的对比判断，对于给定的两个数lft，rgt，误区是直接 lft rgt 判断，根据题目的思路，介意将rgt 接到 lft后面， 与lft 接到 rgt 后面来对比，这样会简单很多，不过这样需要考虑到是否会溢出的问题，题目的验证好像没有对这一问题的严格控制，可以将相接的数值使用 unsigned long int 来存储，这样避免一定情况的溢出。

#include <vector>
#include <iostream>
#include <algorithm>
#include <sstream>
using namespace std;

class Solution {
public:
    string largestNumber(vector<int> &num) {
        struct MyCompared
        {
            bool operator ()(int lft,int rgt)
            {
                long unsigned int lidx=1,ridx=1;
                while(lidx!=1000000000)
                    if(lft>=10*lidx)  lidx*=10;
                    else    break;
                while(ridx!=1000000000)
                    if(rgt>=10*ridx)  ridx*=10;
                    else    break;
                lidx*=10;
                ridx*=10;
                return lft*ridx+rgt > rgt*lidx+lft;
            }
        }myCompared;
        if(num.size()==0)   return "";
        sort(num.begin(),num.end(),myCompared);
        ostringstream os;
        if(num[0]==0)   return "0";
        for(int i =0;i<num.size();i++)
            os<<num[i];
        return os.str();
    }
};

int main()
{
    vector<int > num{10,2};
    Solution sol;
    cout<<sol.largestNumber(num)<<endl;
    return 0;
}