1. two sum

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        int index_1 = 0;
        int index_2 = 0;
        for(int i = 0; i < nums.length; i++) {
            for(int j = i + 1; j < nums.length; j++) 
                if(nums[i] + nums[j] == target) {
                    index_1 = i;
                    index_2 = j;
                    break;
                }
        }
        return new int[]{index_1,index_2};
    }
}