[leetcode] Largest Number

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本文介绍了一个利用排序算法和字符串比较方法解决排列组合问题，具体目标是在给定整数数组中找到能够组成最大数值的排列方式。通过自定义比较函数，将整数转换为字符串进行排序，从而实现数组元素的重新排列，最终返回最大可能的数字字符串。重点在于理解如何在编程中灵活运用排序技巧和字符串操作，以解决实际问题。

From : https://leetcode.com/problems/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.

class Solution {
public:
    static int comp(int a, int b) {
		string sa = to_string(a);
		string sb = to_string(b);
		return sa+sb > sb+sa;
    }
    string largestNumber(vector<int>& nums) {
        if(nums.size() == 0) return "";
		sort(nums.begin(), nums.end(), comp);
        string ans = "";
        for(int i=0, l=nums.size(); i<l; i++) {
			ans += to_string(nums[i]);
        }
        if(ans[0] == '0') return "0";
        return ans;
    }
};

public class Solution {
    public String largestNumber(int[] nums) {
        if (nums == null || nums.length == 0) {
			return "";
		}
		String[] strs = new String[nums.length];
		for (int i = 0; i < nums.length; ++i) {
			strs[i] = String.valueOf(nums[i]);
		}

		Arrays.sort(strs, new Comparator<String>() {
			public int compare(String a, String b) {
				return (b + a).compareTo(a + b);
			}
		});
		
		if(strs[0].equals("0")) {
		    return "0";
		}
		StringBuilder sb = new StringBuilder();
		for (String s : strs) {
			sb.append(s);
		}
		return sb.toString();
    }
}