[LeetCode]525. Contiguous Array

https://leetcode.com/problems/contiguous-array/#/description

01序列数组，找出0和1个数相同的最长子数组长度

将0置为-1，找和为0的sum(i, j)。用HashMap保存第一个和为sum的位置map.put(sum, i)。问题变形为求前缀和为0的最长子数组。

public class Solution {    public int findMaxLength(int[] nums) {        for (int i = 0; i < nums.length; i++) {            if (nums[i] == 0) {                nums[i] = -1;            }        }        int max = 0;        int sum = 0;        HashMap<Integer, Integer> map = new HashMap();        map.put(0, -1);        for (int i = 0; i < nums.length; i++) {            sum += nums[i];            if (map.containsKey(sum)) {                max = Math.max(max, i - map.get(sum));            } else {                map.put(sum, i);            }        }        return max;    }}