128 Largest Number (自定义比较函数排序)

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 is9534330.

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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本题的关键在于写出sort函数的自定义排序方法，参考[C++]LeetCode: 128 Largest Number (自定义比较函数排序)写的方法，非常的通俗易懂。

对于sort的自定义比较函数

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

当需要a排前面，b排后面返回true，若需要b排前面，a排后面则需要返回false.显然上面是要a+b比b+a大时把a排前面。

    bool less_int(int a,int b){

        return b<a;

    }

显然上面是a>b时，a排前面。即按大到小的排。

    bool less_int(int a,int b){

        return b>a;

    }

按小到大的排。

代码：

class Solution {
public:
   static bool cmp(string a,string b)
    {
        return a+b>b+a;
    }
    string largestNumber(vector<int>& nums) {
        vector<string> v1;
        for(auto p:nums)
        v1.push_back(to_string(p));
        sort(v1.begin(),v1.end(),cmp);
    
        string result="";
        for(auto p:v1)
        result+=p;
        if(result[0]=='0') return "0";
        return result;
    }
};