【哈希】1.两数之和

题目：https://leetcode.cn/problems/two-sum/description/?envType=study-plan-v2&envId=top-100-liked

Python3

解法1

这样我们创建一个哈希表，对于每一个 x，我们首先查询哈希表中是否存在 target - x，然后将 x 插入到哈希表中，即可保证不会让 x 和自己匹配

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        tmp_dict = dict() # val => index
        for i in range(len(nums)):
            res = target - nums[i]
            if res in tmp_dict:
                return list([tmp_dict[res], i])
            else:
                tmp_dict[nums[i]] = i
        return list()

Java

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; ++i) {
            if (map.containsKey(target - nums[i])) {
                return new int[]{map.get(target - nums[i]), i};
            } else {
                map.put(nums[i], i);
            }
        }

        return new int[0];
    }
}