Question

Formatted question description: https://leetcode.ca/all/179.html

 179. Largest Number

 Given a list of non negative integers, arrange them such that they form the largest number.

 Example 1:

 Input: [10,2]
 Output: "210"

 Example 2:

 Input: [3,30,34,5,9]
 Output: "9534330"

 Note: The result may be very large, so you need to return a string instead of an integer.

 @tog-top100

Algorithm

For two numbers a and b, if you convert them to strings, if ab> ba, then a will be ranked first,

For example, 9 and 34, since 934>349, 9 is in front,
For example, 30 and 3, because 303<330, 3 is in front of 30.

After sorting the original array according to this rule, converting each number into a string and then concatenating it is the final result.

Code

Java

import java.util.Arrays;
import java.util.Comparator;

public class Largest_Number {
    class Solution {

        public String largestNumber(int[] nums) {
            // Get input integers as strings.
            String[] asStrs = new String[nums.length];
            for (int i = 0; i < nums.length; i++) {
                asStrs[i] = String.valueOf(nums[i]);
            }

            // Sort strings according to custom comparator.
            Arrays.sort(asStrs, new LargerNumberComparator());

            // If, after being sorted, the largest number is `0`, the entire number
            // is zero.
            if (asStrs[0].equals("0")) {
                return "0";
            }

            // Build largest number from sorted array.
            String largestNumberStr = new String();
            for (String numAsStr : asStrs) {
                largestNumberStr += numAsStr;
            }

            return largestNumberStr;
        }

        private class LargerNumberComparator implements Comparator<String> {
            @Override
            public int compare(String a, String b) {
                String order1 = a + b;
                String order2 = b + a;
                return order2.compareTo(order1);
            }
        }

    }
}

// OJ: https://leetcode.com/problems/largest-number/
// Time: O(NlogN * W) where W is the max length of the number strings.
// Space: O(NW)
class Solution {
public:
    string largestNumber(vector<int>& A) {
        vector<string> v;
        for (int n : A) v.push_back(to_string(n));
        sort(begin(v), end(v), [](auto &a, auto &b) {
            for (int i = 0; i < a.size() + b.size(); ++i) {
                char x = i < a.size() ? a[i] : b[i - a.size()], y = i < b.size() ? b[i] : a[i - b.size()];
                if (x != y) return x > y;
            } 
            return false; // don't return true which will result in infinite loop
        });
        if (v[0] == "0") return "0";
        string ans;
        for (auto &s : v) ans += s;
        return ans;
    }
};

class Solution:
  # @param {integer[]} nums
  # @return {string}
  def largestNumber(self, nums):
    def cmpFunc(a, b):
      stra, strb = str(a), str(b)
      if stra + strb < strb + stra:
        return -1
      elif stra + strb > strb + stra:
        return 1
      else:
        return 0

    nums.sort(cmp=cmpFunc, reverse=True)
    return "".join(str(num) for num in nums) if sum(nums) != 0 else "0"

179 - Largest Number

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