leetcode第一题

aimeng1981

于 2017-06-11 17:13:00 发布

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/dailinfu/p/6985666.html

本文详细解析了一种解决两数之和问题的高效算法，通过使用哈希表记录元素及其下标，实现快速查找目标补数，避免了双重循环的高时间复杂度，大大提升了算法效率。

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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].

public class Solution {
    public int[] twoSum(int[] nums, int target) {
            if(nums.length<2)
            return nums;
            int[] arr=new int[2];
            Map<Integer,Integer> map=new HashMap<Integer,Integer>();
            for(int i=0;i<nums.length;i++)
            {
                if(!map.containsKey(nums[i])){
                map.put(nums[i],i);
                }
                if(map.containsKey(target-nums[i])&&i!=map.get(target-nums[i]))
                {
                    arr[0]=map.get(target-nums[i]);
                    arr[1]=i;
                      return arr;   
                }
              
            }
      return arr;      
    }
}