1.TwoSum Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].

判斷陣列中是否存在兩數，使得兩數相加得到目標結果，返回兩數下標

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