[LeetCode] Find Anagram Mappings

Given two lists Aand B, and B is an anagram of A. B is an anagram of A means B is made by randomizing the order of the elements in A.

We want to find an index mapping P, from A to B. A mapping P[i] = j means the ith element in A appears in B at index j.

These lists A and B may contain duplicates. If there are multiple answers, output any of them.

For example, given

A = [12, 28, 46, 32, 50]
B = [50, 12, 32, 46, 28]

We should return

[1, 4, 3, 2, 0]

as P[0] = 1 because the 0th element of A appears at B[1], and P[1] = 4 because the 1st element of A appears at B[4], and so on.

Note:

1. A, B have equal lengths in range [1, 100].
2. A[i], B[i] are integers in range [0, 10^5].

找出数组A中元素在B中出现位置的索引。如果B中不存在A中元素，则返回0。

思路：这道题是map的简单应用，用map存储B中元素及对应的索引。然后遍历A中元素在map中查找即可。

class Solution {
public:
    vector<int> anagramMappings(vector<int>& A, vector<int>& B) {
        unordered_map<int, int> m;
        vector<int> res;
        for (int i = 0; i < B.size(); i++)
            m[B[i]] = i;
        for (auto& a : A) {
            if (m.count(a)) {
                res.push_back(m[a]);
            }
            else {
                res.push_back(0);
            }
        }
        return res;
    }
};
// 6 ms