Java 练习1--数组

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 thesame element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

解决代码：

public int[] twoSum(int[] numbers, int target) {        int[] result = new int[2];        Map<Integer, Integer> map = new HashMap<Integer, Integer>();        for (int i = 0; i < numbers.length; i++) {            if (map.containsKey(target - numbers[i])) {                result[1] = i + 1;                result[0] = map.get(target - numbers[i]);                return result;            }            map.put(numbers[i], i + 1);        }        return result;    }

解释：将数组值逐一放入map中，然后用后面的数据进行比较，是否存在之和为给定值，若存在则返回。

复杂度o(n)。