LeetCode1 Two Sum

题目：

       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].

public class TwoSum {
    public int[] twoSum(int[] nums, int target) {
        if (nums == null || nums.length < 2)
            return null;

        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            map.put(nums[i],i);
        }
        int[] res = null;
        for (int i = 0; i < nums.length; i++) {
            if (map.containsKey(target - nums[i]) && i != map.get(target - nums[i])){
                res = new int[2];
                res[0] = i;
                res[1] = map.get(target - nums[i]);
                return res;
            }
        }

        return res;
    }

    public static void main(String[] args) {
        int[] nums = {2, 7, 11, 15};
        int target = 9;
        System.out.println(Arrays.toString(new TwoSum().twoSum(nums, target)));
    }
}

public class TwoSum {
    public int[] twoSum(int[] nums, int target) {
        if (nums == null || nums.length < 2)
            return null;

        Map<Integer, Integer> map = new HashMap<>(nums.length, 1.0F);
        for (int i = 0; i < nums.length; i++) {
            if (map.containsKey(nums[i])) {
                return new int[] { map.get(nums[i]), i };
            }
            map.put(target-nums[i], i);
        }
        throw new IllegalArgumentException("No two sum solution");
    }

    public static void main(String[] args) {
        int[] nums = {2, 7, 11, 15};
        int target = 9;
        System.out.println(Arrays.toString(new TwoSum().twoSum(nums, target)));
    }
}