[leetcode] Hash Table-760. Find Anagram Mappings

chenhan233

于 2018-01-13 09:30:58 发布

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本文介绍了一种算法，用于解决两个相同元素组成的列表之间的索引映射问题。通过使用哈希表，可以快速找到一个列表中元素在另一个列表中的位置。

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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:

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

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;
    }
};