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[LeetCode] 1122. Relative Sort Array #1122

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grandyang opened this issue May 30, 2019 · 0 comments
Open

[LeetCode] 1122. Relative Sort Array #1122

grandyang opened this issue May 30, 2019 · 0 comments

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@grandyang
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grandyang commented May 30, 2019

Given two arrays arr1 and arr2, the elements of arr2 are distinct, and all elements in arr2 are also in arr1.

Sort the elements of arr1 such that the relative ordering of items in arr1 are the same as in arr2.  Elements that don't appear in arr2 should be placed at the end of arr1 in ascending order.

Example 1:

Input: arr1 = [2,3,1,3,2,4,6,7,9,2,19], arr2 = [2,1,4,3,9,6]
Output: [2,2,2,1,4,3,3,9,6,7,19]

Constraints:

  • 1 <= arr1.length, arr2.length <= 1000
  • 0 <= arr1[i], arr2[i] <= 1000
  • All the elements of arr2 are distinct.
  • Each arr2[i] is in arr1.

这道题说是有两个数组 arr1 和 arr2,其中 arr2 中的所有数字均在 arr1 中,现在让给 arr1 重新排序,使得其按照 arr2 中数字的顺序排列,将不在 arr2 中的数字按照大小顺序排在末尾,题目中给的例子可以很好的帮助我们理解题意。由于 arr1 中可能出现重复数字,而相同的数字是要排在一起的,所以需要统计 arr1 中每个数字出现的次数,又因为最后还需要将不在 arr2 中的数字按顺序排列,那么这里用个 TreeMap 是坠好的,既能统计个数,又能排序,简直太棒了。用 TreeMap 统计好 arr1 中数字的个数之后,然后遍历 arr2,将其中每个数字在之前的 TreeMap 中找到对应的次数,并在结果 res 中加入相同次数的数字进去,之后在 TreeMap 中移除该数字。这样遍历完 arr2 之后,在 TreeMap 中剩下的数字就是仅存在于 arr1 的,且还是有序的,可以直接按顺序加入到结果 res 中即可,参见代码如下:

class Solution {
public:
    vector<int> relativeSortArray(vector<int>& arr1, vector<int>& arr2) {
		vector<int> res;
		map<int, int> m;
		for (int num : arr1) ++m[num];
		for (int num : arr2) {
			for (int i = 0; i < m[num]; ++i) {
				res.push_back(num);
			}
			m.erase(num);
		}
		for (auto a : m) {
			for (int i = 0; i < a.second; ++i) {
				res.push_back(a.first);
			}
		}
		return res;
    }
};

Github 同步地址:

#1122

参考资料:

https://leetcode.com/problems/relative-sort-array/

https://leetcode.com/problems/relative-sort-array/discuss/335056/Java-in-place-solution-using-counting-sort

https://leetcode.com/problems/relative-sort-array/discuss/334585/Python-Straight-Forward-1-line-and-2-lines

LeetCode All in One 题目讲解汇总(持续更新中...)

@grandyang grandyang changed the title [LeetCode] 1122. Missing Problem [LeetCode] 1122. Relative Sort Array Jul 3, 2021
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