public class Solution {
public int maxLength (int[] arr) {
int[] last = new int[100000];
int n = arr.length;
int res = 0;
int start = 0; // 窗口开始位置
for(int i = 0; i < n; i++) {
int index = arr[i];
start = Math.max(start, last[index]);
res = Math.max(res, i - start + 1);
last[index] = i+1;
}