区间统计【美团18.09.06校招笔试】

思路：

1. 简单点的，暴力就完事了，但是会超时
2. 利用滑动窗口思想，利用List模拟一个窗口，在窗口中利用map存储数字出现的次数，每次窗口移动遍历map判断是否有数出现的次数达到阈值t

//暴力法 只能通过82%
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
while (in.hasNext()) {
Map<Integer, Integer> map = new TreeMap<>();
int res = 0;
int n = in.nextInt();
int k = in.nextInt();
int t = in.nextInt();
int[] arr = new int
;
for (int i = 0; i < n; i++) {
arr[i] = in.nextInt();
}
for (int i = 0, j = i + k - 1; j < n; i++, j++) {
for (int p = i; p <= j; p++) {
if (map.containsKey(arr[p])) {
map.put(arr[p], map.get(arr[p]) + 1);
} else {
map.put(arr[p], 1);
}
}
if (isT(map, t)) {
res++;
}
map.clear();
}
System.out.println(res);
}
}

private static boolean isT(Map<Integer, Integer> map,int t) {
for (Integer key : map.keySet()) {
int value = map.get(key);
if (value >= t) {
return true;
}
}
return false;
}

//滑动窗口法
public class Main {

static class Node {
int index;
int value;

Node(int index, int value) {
this.index = index;
this.value = value;
}
}

public static void main(String[] args) {
Scanner in = new Scanner(System.in);
while (in.hasNext()) {
int n = in.nextInt();
int k = in.nextInt();
int t = in.nextInt();

int[] arr = new int
;
for (int i = 0; i < arr.length; i++) {
arr[i] = in.nextInt();
}
//用一个List来模拟窗口
LinkedList<Node> list = new LinkedList<>();
//value：times利用map来统计每个value出现的次数
HashMap<Integer, Integer> map = new HashMap<>();
int end = 0;
int res = 0;//统计次数
while (end < arr.length) {
if (list.size() < k) {
list.add(new Node(end, arr[end]));
addNode(map,arr,end);
end++;
}

if (list.size() == k) {
//统计出现的次数有没有大于t
int temptimes = 0;
for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
temptimes = Math.max(temptimes, entry.getValue());
}
if (temptimes >= t) {
res++;
}

//弹出list最前面的值
Node node = list.poll();
if (map.get(node.value) == 1) {
map.remove(node.value);
}else {
//出现次数-1
map.put(node.value, map.get(node.value) - 1);
}
}
}
System.out.println(res);
}
}

private static void addNode(HashMap<Integer,Integer> map,int arr[],int end) {
if (!map.containsKey(arr[end])) {
map.put(arr[end], 1);
}else {
map.put(arr[end], map.get(arr[end])+1);
}
}
}