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001. Two Sum

难度: Easy

刷题内容

原题连接

  • https://leetcode.com/problems/two-sum

内容描述

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].

解题方案

思路 1 **- 时间复杂度: O(N)*- 空间复杂度: O(N)***

算法来源于知乎文章——趣味算法思想

先定义一个Object类型的数据结构obj,它的key为target - numbers[i](比如数组第一项为2),value为索引。然后每次都看看obj[numbers[i]] 是否存在,如果存在,那我们就找到了这样的一组数据,返回当前索引以及obj[numbers[i]]。

代码:

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
   var obj = {};

  for(var i=0; i< nums.length;i++) {
    const item = nums[i];
    if(obj[item] >= 0) {
      return [obj[item], i]
    } else {
      obj[target - item] = i;
    }
  }
};


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