Two-sum

###Question

###Analysis
给定一个整数数组，在其中找两个数，两数满足其和为一个随机的整数且这两个数不等，返回这两个数的下标。

Answers

• Brute Force

  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[j]==target-nums[i]){
          return new int[]{i,j};
         }
        }
      }
     throw new IllegalArgumentException("No two sum solution");
  }

• Two-pass Hash Table

  public int[] twoSum(int[] nums,int target){
    Map<Integer,Integer> map=new HashMap<>();
    for (int i=0;i<nums.length;i++){
      map.put(nums[i],i);
    }
    for (int i=0;i<nums.length;i++){
      int complement=target-nums[i];
      if (map.containsKey(complement)&&map.get(complement !=i){
        return new int[]{i;map.get(complement)};
      }
    }
    throw new IliegalArgumentException("No two sum solution");
  }

• One-pass Hash Table

  public int[] twoSum (int[] nums,int target){
  Map<Integer, Integer> map=new HashMap<>();
  for(int i=0;i<nums.length;i++){
    int complement=target-nums[i];
    if (map.containsKey(complement)){
      return new int[]{map.get(complement);i};
    }
    map.put(nums[i];i);
  }
  throw new IllegalArgumentException("No two sum solution");
  }