最简单的想法就是双指针遍历，两个下标的值相加等于target就可以返回了

class Solution {

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

        int[] res =new int[2];

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

            for (int j = i +1; j < nums.length; j++) {

                if (nums[j] + nums[i] == target) {

                    res[0] = i;

                    res[1] = j;

                    return res;

                }

            }

        }

        return res;

    }

}

还有一种方法就是用map保存下标的方式，数组的值作为key，下标的值作为value，进行查找

class Solution {

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

        Map<Integer,Integer> map=new HashMap<>();

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

            int temp=target-nums[i];

            if(map.containsKey(temp)){

                return new int[]{map.get(temp),i};

            }

            map.put(nums[i],i);

        }

        return null;

    }

}