LeetCode-1:两数之和(Java语言实现)

class Solution {
    public int[] twoSum(int[] arr, int target) {
        if (arr == null){
        return null;
        }
        HashMap<Integer,Integer> map = new HashMap<>();
        for(int i = 0; i < arr.length ; i++){
            if (map.containsKey(target - arr[i])){
                return new int[]{map.get(target - arr[i]),i};
            }
            map.put(arr[i],i);
        }
        return new int[]{-1,-1};
    }
}