525. Contiguous Array

Given a binary array, find the maximum length of a contiguous subarray with equal number of 0 and 1.

Example 1:

Input: [0,1]Output: 2Explanation: [0, 1] is the longest contiguous subarray with equal number of 0 and 1.

Example 2:

Input: [0,1,0]Output: 2Explanation: [0, 1] (or [1, 0]) is a longest contiguous subarray with equal number of 0 and 1.

Note: The length of the given binary array will not exceed 50,000.

public class Solution {    public int findMaxLength(int[] nums) {        if(nums == null || nums.length == 0){            return 0;        }        for(int i=0; i<nums.length; i++){            if(nums[i] == 0){                nums[i] = -1; //先把所有的0变成-1，这样就是求sum为0的最大区间            }        }        int sum = 0, max = 0;        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();        map.put(0, -1);        for(int i=0; i<nums.length; i++){            sum += nums[i];            if(!map.containsKey(sum)){                map.put(sum, i);            }else{                max = Math.max(max, i-map.get(sum));            }        }        return max;    }}