题解：

import java.util.HashMap;
import java.util.Map;

public class Test {
    //暴力解决法
    public  static int[] twoSum(int[] nums, int target) {
        for(int i=0;i<nums.length;i++){
            for(int j=i+1;j<nums.length;j++){
                if(nums[i]+nums[j]==target){
                    int[] indexs={0,0};
                    indexs[0]=i;
                    indexs[1]=j;
                    return indexs;
                }
            }
        }
        return null;
    }
    //哈希表解决发
    public  static int[] twoSump(int[] nums, int target) {
        Map<Integer,Integer> hashtable=new HashMap<>();
        for(int i=0;i<nums.length;++i){
            if(hashtable.containsKey(target-nums[i])){
                return new int[]{hashtable.get(target-nums[i]),i};
            }
            hashtable.put(nums[i],i);
        }
        return null;
    }
    //测试
    public static void main(String[] args) {
        int[] nums={2,4,5,7};
        int target=9;
//        int targets[]=twoSum(nums,target);
        int targets[]=twoSump(nums,target);
        for(int i:targets){
            System.out.println(i);
        }
    }
}