1409. Queries on a Permutation With Key

Given the array queries of positive integers between 1 and m, you have to process all queries[i] (from i=0 to i=queries.length-1) according to the following rules:

• In the beginning, you have the permutation P=[1,2,3,...,m].
• For the current i, find the position of queries[i] in the permutation P (indexing from 0) and then move this at the beginning of the permutation P. Notice that the position of queries[i] in P is the result for queries[i].

Return an array containing the result for the given queries.

Example 1:

Input: queries = [3,1,2,1], m = 5
Output: [2,1,2,1] 
Explanation: The queries are processed as follow: 
For i=0: queries[i]=3, P=[1,2,3,4,5], position of 3 in P is 2, then we move 3 to the beginning of P resulting in P=[3,1,2,4,5]. 
For i=1: queries[i]=1, P=[3,1,2,4,5], position of 1 in P is 1, then we move 1 to the beginning of P resulting in P=[1,3,2,4,5]. 
For i=2: queries[i]=2, P=[1,3,2,4,5], position of 2 in P is 2, then we move 2 to the beginning of P resulting in P=[2,1,3,4,5]. 
For i=3: queries[i]=1, P=[2,1,3,4,5], position of 1 in P is 1, then we move 1 to the beginning of P resulting in P=[1,2,3,4,5]. 
Therefore, the array containing the result is [2,1,2,1].  

Example 2:

Input: queries = [4,1,2,2], m = 4
Output: [3,1,2,0]

Example 3:

Input: queries = [7,5,5,8,3], m = 8
Output: [6,5,0,7,5]

Constraints:

• 1 <= m <= 10^3
• 1 <= queries.length <= m
• 1 <= queries[i] <= m

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初始时给定一个P=[1,2,…,m]的数组，然后有一个queries数组，对于每一个query，问其在P中的下标，并且将该元素移到P的开头，最后问queries数组中所有query的下标的数组。

模拟题，由于有元素的移动操作，即删除和插入操作，所以这里借用链表来处理。完整代码如下：

class Solution {
public:
	vector<int> processQueries(vector<int>& queries, int m) {
		list<int> lst;
		for (int i = 1; i <= m; ++i)lst.push_back(i);
		vector<int> ans;
		for (int i = 0; i < queries.size(); ++i) {
			int val = queries[i];
			int j = 0;
			list<int>::iterator it = lst.begin();
			while (it != lst.end()) {
				if (*it == val) {
					ans.push_back(j);
					lst.erase(it);
					lst.push_front(val);
					break;
				}
				else {
					++it;
					++j;
				}
			}
		}
		return ans;
	}
};

本代码提交AC，用时28MS。