Two Sum

1.hashMap方法O(n)空间换时间

public class Solution {

    public int[] twoSum(int[] numbers, int target) {

        HashMap<Integer,Integer> hash=new HashMap<Integer,Integer>();

        int ans[]=new int[2];

        for(int i=0;i<numbers.length;i++)

        {

            if(hash.containsKey(target-numbers[i]))

            {

                ans[0]=hash.get(target-numbers[i])+1;

                ans[1]=i+1;

                return ans;

                

            }

            else hash.put(numbers[i],i);

            

        }

            

        

        return ans;

    }

}

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2. 排序后获取两个值

class node implements Comparable<node>

{

    int x;

    int y;

    public int compareTo(node n)

    {

        return this.x-n.x;

        

        

    }

    public node(int x,int y)

    {

        this.x=x;

        this.y=y;

        

    }

}

public class Solution {

    

    public int[] twoSum(int[] numbers, int target) {

        node n[]=new node[numbers.length];

        for(int j=0;j<numbers.length;j++)

        {

            n[j]=new node(numbers[j],j+1);

        }

        Arrays.sort(n);

            

        

        int ans[]=new int[2];

        int low=0;

        int high=numbers.length-1;

        while(low<high)

        {

            int sum=n[low].x+n[high].x;

            if(sum==target)

            {

                ans[0]=n[low].y;

                ans[1]=n[high].y;

                if(n[low].y>n[high].y)

                {

                    ans[0]=n[high].y;

                    ans[1]=n[low].y;

                }

           

             break;

            }

            else if(sum>target) high--;

            else  low++;

           

            

            

            

        }

        

        return ans;

       

    }

}