Subarray Sum java solution (prefix sum)

Subarray sum

description:

Given an integer array, find a subarray where the sum of numbers is zero. Your code should return the index of the first number and the index of the last number.

Notice

There is at least one subarray that it’s sum equals to zero.

Example
Given [-3, 1, 2, -3, 4], return [0, 2] or [1, 3].

* 使用prefix sum的方法进行处理，首先使用map的来进行存储数据，当下一个数据与所存储的数据相同时，说明出现了下一个的0 此时使用arraylist来进行存储。时间复杂度O(n), 空间复杂度O(n) *

public class Solution {    /**     * @param nums: A list of integers     * @return: A list of integers includes the index of the first number      *          and the index of the last number     */    public ArrayList<Integer> subarraySum(int[] nums) {        // write your code here        ArrayList<Integer> arr = new ArrayList<>();        if (nums == null || nums.length == 0) {            return null;        }        Map<Integer, Integer> map = new HashMap<>();        map.put(0, -1);        int sum = 0;        for (int i = 0; i < nums.length; i++) {            sum += nums[i];            if (map.containsKey(sum)) {                arr.add(map.get(sum) + 1);                arr.add(i);                return arr;            }            map.put(sum, i);        }        return arr;    }}