LeetCode Top 100 Liked Questions 1. Two Sum(Java版； Easy)

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LeetCode Top 100 Liked Questions 1. Two Sum(Java版; Easy)

题目描述

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

思路

• 使用哈希表
• 遍历数组中的每个元素

• 如果target-nums[i]在哈希表中, 则返回哈希表中对应的结果及i
• 如果target-nums[i]不在哈希表中, 则将nums[i]和i加入哈希表,继续下一轮循环

• 如果循环结束,说明没有找到结果,返回null

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