599. Minimum Index Sum of Two Lists

599. Minimum Index Sum of Two Lists

Suppose Andy and Doris want to choose a restaurant for dinner, and they both have a list of favorite restaurants represented by strings.

You need to help them find out their common interest with the least list index sum. If there is a choice tie between answers, output all of them with no order requirement. You could assume there always exists an answer.

Example 1:

Input: ["Shogun", "TapiocaExpress", "Burger King", "KFC"] ["Piatti", "The Grill at TorreyPines", "Hungry Hunter Steakhouse", "Shogun"] Output:["Shogun"] Explanation: The only restaurant they both like is"Shogun". 

Example 2:

Input: ["Shogun", "TapiocaExpress", "Burger King", "KFC"] ["KFC", "Shogun", "Burger King"]Output: ["Shogun"] Explanation: The restaurant they bothlike and have the least index sum is "Shogun" with index sum 1 (0+1).

Note:

1. The length of both lists will be in the range of [1, 1000].
2. The length of strings in both lists will be in the range of [1, 30].
3. The index is starting from 0 to the list length minus 1.
4. No duplicates in both lists.

题目大意：
有两个字符串数组，找到他们当中相同的字符串，并求两个字符串的索引（数组的下标） 之和。把那些索引之和最小的字符串输出来。
注意，两个数组内没有相互重复的字符串。

思路：
看了Discuss中的方法。使用HashMap空间换时间，能够达到O(n+m)的复杂度。

首先，使用一个HashMap保存第一个字符串数组，key对应字符串，value对应索引。

然后，遍历第二个字符串，如果在HashMap中存在，则求索引之和，并记录到HashMap2中，key对应字符串，value对应索引之和。同时记录当前最小的索引值，记为min

最后，遍历HashMap2，把value等于min的全部输出

Java代码：

public class Solution {    public String[] findRestaurant(String[] list1, String[] list2) {        HashMap<String, Integer> map1 = new HashMap<>();        HashMap<String, Integer> map2 = new HashMap<>();        for(int i = 0; i < list1.length; i++) {            map1.put(list1[i], i);        }        int min = Integer.MAX_VALUE;        for(int i = 0; i < list2.length; i++) {            if( map1.containsKey(list2[i]) ) {                int index_sum = map1.get(list2[i]) + i;                min = Math.min(index_sum, min);                map2.put(list2[i], index_sum);            }        }        List<String> list = new ArrayList<>();         for(String key : map2.keySet()) {            if(min == map2.get(key)) {                list.add(key);            }        }        return list.toArray(new String[list.size()]);    }}