Force buckle - sum of two numbers

Power button - Sum of two numbers

One 、 subject

Given an array of integers nums  And an integer target value target, Please find... In the array And is the target value target   the   Two   Integers , And return their array subscripts .

You can assume that each input corresponds to only one answer . however , The same element in the array cannot be repeated in the answer .

You can return the answers in any order .

Example 1：

Input ：nums = [2,7,11,15], target = 9
Output ：[0,1]
explain ： because nums[0] + nums[1] == 9 , return [0, 1] .
Example 2：

Input ：nums = [3,2,4], target = 6
Output ：[1,2]
Example 3：

Input ：nums = [3,3], target = 6
Output ：[0,1]

Two 、 solution 1

    public int[] twoSum1(int[] nums, int target) {
        int[] indexs = new int[2];
        //  Double cycle   The cycle limit is (n^2-n)/2
        for (int i = 0; i < nums.length; i++) {
            for (int j = nums.length - 1; j > i; j--) {
                if (nums[i] + nums[j] == target) {
                    indexs[0] = i;
                    indexs[1] = j;
                    System.out.println(Arrays.toString(indexs));
                    return indexs;
                }
            }
        }
        return indexs;
    }

3、 ... and 、 solution 2

public int[] twoSum3(int[] nums, int target) {
        int[] indexs = new int[2];
        //  establish k-v , One to one hash table 
        HashMap<Integer, Integer> hash = new HashMap<Integer, Integer>();
        for (int i = 0; i < nums.length; i++) {
            if (hash.containsKey(nums[i])) {
                indexs[0] = i;
                indexs[1] = hash.get(nums[i]);
                System.out.println(Arrays.toString(indexs));
                return indexs;
            }
            //  Store data  key Complement number  ,value Subscript 
            hash.put(target - nums[i], i);
        }
        return indexs;
    }