LeetCode - Largest Number

Largest Number

2015.1.23 20:24

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.

Solution:

　　Sort the numbers and piece them together, you'll get the answer, either largest or smallest. As for how to sort them, please see the comparator().

　　Time complexity is O(n * log(n)), space complexity may be the same, or less.

Accepted code:

//#define ZZ
#include <algorithm>
#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
using namespace std;

bool comparator(const string &s1, const string &s2)
{
    string s12, s21;

    s12 = s1 + s2;
    s21 = s2 + s1;

    bool res = s12 < s21;
    s12.clear();
    s21.clear();

    return res;
}

class Solution {
public:
    string largestNumber(vector<int> &num) {
        char s[100];
        vector<string>vs;

        int n, i;

        n = (int)num.size();
        for (i = 0; i < n; ++i) {
            sprintf(s, "%d", num[i]);
            vs.push_back(string(s));
        }

        sort(vs.begin(), vs.end(), comparator);
        string res = "";

        for (i = n - 1; i >= 0; --i) {
            res += vs[i];
        }
        vs.clear();

        i = 0;
        n = (int)res.length();
        while (i < n - 1 && res[i] == '0') {
            ++i;
        }
        res = res.substr(i, n - i);

        return res;
    }
};

#ifdef ZZ
int main()
{
    vector<int> num;
    int n;
    int i;
    Solution sol;

    while (cin >> n) {
        num.resize(n);
        for (i = 0; i < n; ++i) {
            cin >> num[i];
        }
        cout << sol.largestNumber(num) << endl;
        num.clear();
    }

    return 0;
}
#endif