public class twosum2 {

    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        twosum2 twosum = new twosum2();   //实例化这个类,第一个是类名，空格后面是实例化的类名
        int[] nums = new int[4];        //输入数组
        int target = 6;
        nums[0] = 1;
        nums[1] = 3;
        nums[2] = 4;
        nums[3] = 5;  
        twosum.Twosum(nums, target);     //调用方法，第一个是实例化的类名，。后面是调用函数名 
        int[] result = twosum.Twosum(nums, target);       //使用调用方法的返回值
        for(int i = 0; i < twosum.Twosum(nums, target).length; ++i){
            System.out.println(result[i]);
        }

    }
//以上是测试部分，以下是算法部分
    public int[] Twosum(int[] nums, int target) {
        int[] result = new int [2];
        for (int i = 0; i < nums.length; i++) {
            for (int j = i + 1; j < nums.length; j++) {
                if (nums[i] + nums[j] == target) {                    
                    result[0] = i + 1;
                    result[1] = j + 1; 
                    break;                    
                }
            }
        }
        return result;
    }
    
}

public class Solution {
    /*
     * @param numbers : An array of Integer
     * @param target : target = numbers[index1] + numbers[index2]
     * @return : [index1 + 1, index2 + 1] (index1 < index2)
     */
    public int[] twoSum(int[] numbers, int target) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < numbers.length; i++) {
            if (map.get(numbers[i]) != null) {
                int[] result = {map.get(numbers[i]), i};
                return result;
            }
            map.put(target - numbers[i], i);
        }
        int[] result = {};
        return result;
    }
}