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: 2
Explanation: [0, 1] is the longest contiguous subarray with equal number of 0 and 1.
Example 2:
Input: [0,1,0]
Output: 2
Explanation: [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.
思路：
本题和maximun size subarray sum equal k比较类似，这里有一个把0转换成-1来进行计算的过程，然后存储一个hashmap用来存放sum，如果接下来的sum在hashmap里面出现过，则说明hashmap里面出现的那个值的索引的开始（不包括索引），到目前的索引的和为0。
class Solution
public int findMaxLength(int[] nums) {
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(0, -1);
int sum = 0;
int max = 0;
for(int i = 0; i < nums.length; i++){
if(nums[i] == 0)
nums[i] = -1;
sum += nums[i];
if(map.containsKey(sum)){
max = Math.max(max, i - map.get(sum));
}else{
map.put(sum, i);
}
}
return
