题目：

给定一个放有字母和数字的数组，找到最长的子数组，且包含的字母和数字的个数相同。

返回该子数组，若存在多个最长子数组，返回左端点下标值最小的子数组。若不存在这样的数组，返回一个空数组。

示例 1:

输入: ["A","1","B","C","D","2","3","4","E","5","F","G","6","7","H","I","J","K","L","M"]

输出: ["A","1","B","C","D","2","3","4","E","5","F","G","6","7"]
示例 2:

输入: ["A","A"]

输出: []
提示：

array.length <= 100000

java代码：

class Solution {
    public String[] findLongestSubarray(String[] array) {
        Map<Integer, Integer> indices = new HashMap<Integer, Integer>();
        indices.put(0, -1);
        int sum = 0;
        int maxLength = 0;
        int startIndex = -1;
        int n = array.length;
        for (int i = 0; i < n; i++) {
            if (Character.isLetter(array[i].charAt(0))) {
                sum++;
            } else {
                sum--;
            }
            if (indices.containsKey(sum)) {
                int firstIndex = indices.get(sum);
                if (i - firstIndex > maxLength) {
                    maxLength = i - firstIndex;
                    startIndex = firstIndex + 1;
                }
            } else {
                indices.put(sum, i);
            }
        }
        if (maxLength == 0) {
            return new String[0];
        }
        String[] ans = new String[maxLength];
        System.arraycopy(array, startIndex, ans, 0, maxLength);
        return ans;
    }
}