[LeetCode] 179. Largest Number

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

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

Example 1:

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

Example 2:

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

Example 3:

Input: nums = [1]
Output: "1"

Example 4:

Input: nums = [10]
Output: "10"

Constraints:

• 1 <= nums.length <= 100
• 0 <= nums[i] <= 109

最大数。

题意是给一个整数数组，请将他们拼接成字符串，返回数字最大的字符串。

思路是需要自己写一个comparator函数比较每两个数字拼接结果的字典序，举个例子，需要比较到底是210的字典序大还是102的字典序大。这道题没什么算法，考察的是是否能自己实现一个自定义的comparator函数。JavaScript因为没有数据类型的限制的关系，可以直接比较两个数字的大小。

时间O(n^2) - sort函数最坏情况下

空间O(n)

Java实现

class Solution {
    public String largestNumber(int[] nums) {
        // corner case
        if (nums == null || nums.length == 0) {
            return "";
        }

        // normal case
        int n = nums.length;
        String[] ss = new String[n];
        for (int i = 0; i < n; i++) {
            ss[i] = "" + nums[i];
        }
        Arrays.sort(ss, (a, b) -> {
            String sa = a + b;
            String sb = b + a;
            return sb.compareTo(sa);
        });

        StringBuilder sb = new StringBuilder();
        for (String s : ss) {
            sb.append(s);
        }
        int len = sb.length();
        int k = 0;
        while (k < len - 1 && sb.charAt(k) == '0') {
            k++;
        }
        return sb.substring(k);
    }
}

JavaScript实现

/**
 * @param {number[]} nums
 * @return {string}
 */
var largestNumber = function (nums) {
    // corner case
    if (nums.every(n => n === 0)) {
        return '0';
    }

    // normal case
    nums.sort((n1, n2) => {
        const s1 = new String(n1);
        const s2 = new String(n2);
        const first = s1 + s2;
        const second = s2 + s1;
        if (first > second) {
            return -1;
        } else if (first < second) {
            return 1;
        } else return 0;
    });
    return nums.join('');
};

LeetCode 题目总结