查找数组中两数之和等于指定的数

public static int[] twoSum1(int[] nums, int target) {
    for (int i = 0; i < nums.length - 1; i++) {
        for (int j = i + 1; j < nums.length; j++) {
            if (nums[i] + nums[j] == target){
                return new int[]{i,j};
            }
        }
    }
    return null;
}

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

public static int[] twoSum2(int[] nums, int target) {
    Map<Integer,Integer> map = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
        int num = target - nums[i];
        if (map.containsKey(num)){
            return new int[]{map.get(num),i};
        }
        map.put(nums[i],i);
    }
    return null;
}