1. 兩數字求和 (Two Sum)

1 題目

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.

Example:

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

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

2 代碼

public class Solution {
    public int[] twoSum(int[] nums, int target) {
		if (nums == null || nums.length < 2) {
			return null;
		}
		Map<Integer, Integer> map = new HashMap<>();

		int copy[] = new int[nums.length];

		for (int i = 0; i < nums.length; i++) {
			copy[i] = target - nums[i];
		}

		int[] sum = { 0, 0 };

		for (int i = 0; i < nums.length; i++) {
			map.put(nums[i], i);
		}

		for (int i = 0; i < copy.length; i++) {
			if (map.containsKey(copy[i])) {
				sum[0] = map.get(copy[i]);
				sum[1] = i;
				if (sum[0] != sum[1]) {
					break;
				}

			}
		}

		return sum;
	}
}