1. 两数之和 @python @java

原题

https://leetcode.cn/problems/two-sum/

思路

用哈希表储存数字和下标

复杂度

时间：O(n)
空间：O(n)

Python代码

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        # 用字典储存数字和下标
        seen = dict()
        for i, n in enumerate(nums):
            if target - n in seen:
                return [i, seen[target-n]]
            seen[n] = i

Java代码

class Solution {
    public int[] twoSum(int[] nums, int target) {
        // 用哈希表储存数字和下标
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();    
        for (int i = 0; i < nums.length; i++) {
            int n = nums[i];
            if (map.containsKey(target - n)) {
                return new int[] {i, map.get(target - n)};                
            }
            map.put(n, i);
        }
        return new int[2];
    }
}