【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]:
        val2IdxDict = {}
        for idx, val in enumerate(nums):
            if target - val in val2IdxDict:
                return [val2IdxDict[target - val], idx]
            else:
                val2IdxDict[val] = idx
        return []

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];
    }
}