题目描述

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

代码

    public static int[] twoSum(int[] nums, int target) {

        if (nums == null || nums.length == 0 || nums.length == 1) {
            return new int[2];
        }

        Map<Integer, Integer> map = new HashMap<Integer, Integer>();

        // key为target - nums[i]，不用担心重复，题目说明只有一个解
        for (int i = 0; i < nums.length; i++) {
            map.put(target - nums[i], i);
        }

        for (int i = 0; i < nums.length; i++) {
            Integer v = map.get(nums[i]);

            // 元素不能使用自身
            if (v != null && v != i) {
                return new int[] { i + 1, v + 1 };
            }
        }

        return null;
    }