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I was working on TwoSum problem of LeetCode Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

Test Case:

[2,7,11,15] 9

[3,2,4] 6

[3,3] 6

MY Code:

import java.util.Arrays;
class Solution {
    public int[] twoSum(int[] nums, int target) {
       Arrays.sort(nums);
        int left = 0;
        int right = nums.length-1;
        for(int i : nums){
            int sum = nums[left]+nums[right];
            if(sum == target)
                return new int[]{left+1,right};
            else if(sum > target)
                right--;
            else
                left++;
        }
        return new int[]{0,0};
    }
}

this code is passing for all the test cases except 2nd test case [2,3,4] 6 and no matter what i done it is not resolving so please someone help me with this.

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  • 1
    Why do you sort nums? It will change indices on values. Commented Jun 19, 2022 at 10:06
  • hi david i also tried without sorting the array but it's failing on 2nd test case only Commented Jun 19, 2022 at 10:09
  • 1
    You assume the sum indicates you need to take one step left or right. If the nums are not in order, that doesn't work. If you sort nums, you lose their original index. Why not use two nested loops and try the various combinations? Commented Jun 19, 2022 at 10:18
  • LeetCode includes hints and solutions to problems, including the TwoSum problem. You can read about it there, it is solved most efficiently with a hashmap. Commented Jun 19, 2022 at 11:09
  • thanks @akarnokd i did tried nested loops and it worked. Commented Jun 19, 2022 at 11:40

1 Answer 1

Reset to default
1

I think you can solve it in a better way.

My solution states that first pick the 0th element of the list; Then in a nested loop check it with the 1st, 2nd, ..., nth element of the list to see if their sum is equal to the target. If it is then return the result if not repeat the loop.

For example in [3,2,4] 6 test case:

  1. Pick 3 and go to nested loop.
  2. Pick 2, is 3 + 2 equal to 6? No, then continue.
  3. Pick 4, is 3 + 4 equal to 6? No, then exit from nested loop.
  4. Now pick 2 and go to nested loop.
  5. Pick 4, is 2 + 4 equal to 6? Yes, You find the answer:)
public class Solution {
    
    public static void main(String[] args) {
        int[] nums = {3, 2, 4};
        int target = 6;
        int[] result = twoSum(nums, target);
        System.out.println(result[0] + ", " + result[1]);
    }
    
    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)
                    return new int[]{i, j};
            }
        }
        return new int[]{-1, -1};
    }

}
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2 Comments

thank you so much @soroush-shemshadi for the effort i did tried working this way and it works can you also explain why have you return int[]{-1,-1}; not just empty array
You're welcome. What to return in case of an error is entirely optional, but the convenient way is to use -1 because no array has an index of -1, and this indicates an error.

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