【leetcode】Largest Number

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.

 

设a有x位，b有y位

如果a排在前面，则

a*10^y+b>b*10^x+a

 

利用该思想进行排序

class Solution {
public:
 
    static bool cmp(int a,int b)
    {
        int digitA=1;
        int digitB=1;
       
        int tmpA=a;
       
        while(tmpA>=10)
        {
            digitA++;
            tmpA/=10;
        }
       
        int tmpB=b;
        while(tmpB>=10)
        {
            digitB++;
            tmpB/=10;
        }
       
        return a*pow(10,digitB)+b>b*pow(10,digitA)+a;
       
    }
 
    string largestNumber(vector<int> &num) {
       
        sort(num.begin(),num.end(),cmp);
       
        string result="";
       
        for(int i=0;i<num.size();i++)  
        {
            result+=to_string(num[i]);
        }
       
        if(result[0]=='0') result="0";
       
        return result;
       
    }
};

另一种方法，先把数字转化为字符串，然后通过字符串拼接去比较，这样cmp函数会好些很多

  

class Solution {
public:

    static bool cmp(string a,string b)
    {
        return a+b>b+a;
    }

    string largestNumber(vector<int> &num) {
        
        int n=num.size();
        vector<string> strNum(n);
        for(int i=0;i<n;i++)
        {
            strNum[i]=to_string(num[i]);
        }
        
        sort(strNum.begin(),strNum.end(),cmp);
        
        string result="";
        
        for(int i=0;i<n;i++)
        {
            result+=strNum[i];
        }
        
        if(result[0]=='0') result="0";
        
        return result;
    }
};