Java

Mister-Hope

/*
 * Runtime: 10 ms, faster than 41.97% of Java online submissions for Two Sum.
 *
 * Memory Usage: 56.5 MB, less than 6.02% of Java online submissions for Two Sum.
 */

import java.util.HashMap;

class Solution {
  public int[] twoSum(int[] nums, int target) {
    HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
    for (int i = 0; i < nums.length; i++) {
      int j = target - nums[i];

      if (map.containsKey(j))
        return new int[] {map.get(j), i};

      map.put(nums[i], i);
    }

    throw new IllegalArgumentException("No solution");
  }
}

lizncu

class Solution {
  public 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};
        }
      }
    }

    throw new IllegalArgumentException("No two sum solution");
  }
}

lmy

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