目录链接：

力扣编程题-解法汇总_分享+记录-CSDN博客

GitHub同步刷题项目：

https://github.com/September26/java-algorithms

原题链接：力扣

描述：

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

解题思路：

* 解题思路：
* 记录每个位置charNum-intNum的值，按照这个值来分组，满足统一条件的两个位置相减，就是符合条件的子数组。
* 构建一个Map<Integer, List<Integer>>的结构，某个位置charNum-intNum的结果，value为满足这个结果的所有位置的集合。
* 这里要特别注意一下diff=0的情况，0的话时候额外填充一个0。
* 然后遍历map的value，取出集合，集合的最后一位减去第一位，就是满足条件的长度。求最长。

代码：

public class MianShi1705 {

    public String[] findLongestSubarray(String[] array) {
        Map<Integer, List<Integer>> map = new HashMap<>();
        int intNum = 0;
        int charNum = 0;
        for (int i = 0; i < array.length; i++) {
            String s = array[i];
            char c = s.toCharArray()[0];
            if ((c >= 'A' && c <= 'Z') || c >= 'a' && c <= 'z') {
                charNum++;
            } else {
                intNum++;
            }
            int diff = charNum - intNum;
            List<Integer> integers = obtainQueue(map, diff);
            if (diff == 0 && integers.size() == 0) {
                integers.add(0);
            }
            integers.add(i + 1);
        }

        int maxLength = 0;
        int maxStart = 0;
        int maxEnd = 0;
        for (int key : map.keySet()) {
            List<Integer> list = map.get(key);
            if (list.size() == 0) {
                continue;
            }
            int length;
            if (list.size() == 1) {
                continue;
            }
            length = list.get(list.size() - 1) - list.get(0);
            if (length > maxLength || (length == maxLength && list.get(0) < maxStart)) {
                maxLength = length;
                maxStart = list.get(0);
                maxEnd = list.get(list.size() - 1);
            }
        }
        if (maxLength == 0) {
            return new String[0];
        }
        String[] strings = Arrays.copyOfRange(array, maxStart, maxEnd);
        return strings;
    }

    private List<Integer> obtainQueue(Map<Integer, List<Integer>> map, int key) {
        List<Integer> integers = map.get(key);
        if (integers == null) {
            integers = new ArrayList<>();
            map.put(key, integers);
        }
        return integers;
    }

}