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.

C++代码实现：

#include<iostream>
#include<string>
#include<vector>
using namespace std;

class Solution {
public:
    string largestNumber(vector<int> &num) {
        if(num.empty())
            return "";
        string ret;
        int i,j;
        while(!num.empty())
        {
            i=0;
            for(j=1;j<(int)num.size();j++)
            {
                if((to_string(num[i])+to_string(num[j]))<(to_string(num[j])+to_string(num[i])))
                    i=j;
            }
            ret+=to_string(num[i]);
            num.erase(num.begin()+i);
        }
        while(ret.size()>1&&ret[0]=='0')
            ret.erase(ret.begin());
        return ret;
    }
};

int main()
{
    Solution s;
    vector<int> vec={3,30,34,5,9};
    cout<<s.largestNumber(vec)<<endl;
}

直接调用STL算法进行排序：

#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
using namespace std;
//不能声明non-static成员函数
bool Mycmp(int n1,int n2)
{
    string s1=to_string(n1);
    string s2=to_string(n2);
    return s1+s2>s2+s1;
}
class Solution
{
public:
    string largestNumber(vector<int> &num)
    {
        if(num.empty())
            return "";
        string ret="";
        sort(num.begin(),num.end(),Mycmp);
//sort(num.begin(),num.end(),[](int n1,int n2){ return to_string(n1)+to_string(n2)>to_string(n2)+to_string(n1);});
        if(num[0]==0)
            return "0";
        for(auto a:num)
            ret+=to_string(a);
        return ret;
    }
//声明为static成员是可以的

static bool Mycmp(int n1,int n2)
{
    string s1=to_string(n1);
    string s2=to_string(n2);
    return s1+s2>s2+s1;
}

}; 
int main() 
{ 
　　Solution s; 
　　vector<int> num= {3,32,321}; 
　　cout<<s.largestNumber(num)<<endl; 
}