diff --git a/MCA算法突击课/第03期/mca_08/Code01_Trie.java b/MCA算法突击课/第03期/mca_08/Code01_Trie.java
index 70bb809..934de06 100644
--- a/MCA算法突击课/第03期/mca_08/Code01_Trie.java
+++ b/MCA算法突击课/第03期/mca_08/Code01_Trie.java
@@ -10,8 +10,11 @@ public class Code01_Trie {
 	class Trie {
 
 		class Node {
+			// 该节点通过了几次
 			public int pass;
+			// 有多少个字符串，以该节点结尾
 			public int end;
+
 			public Node[] nexts;
 
 			public Node() {
diff --git a/MCA算法突击课/第03期/mca_08/Code03_PrefixAndSuffixSearch.java b/MCA算法突击课/第03期/mca_08/Code03_PrefixAndSuffixSearch.java
index 485f352..b20b987 100644
--- a/MCA算法突击课/第03期/mca_08/Code03_PrefixAndSuffixSearch.java
+++ b/MCA算法突击课/第03期/mca_08/Code03_PrefixAndSuffixSearch.java
@@ -16,7 +16,10 @@ public class Code03_PrefixAndSuffixSearch {
 	class WordFilter {
 
 		class TrieNode {
+			//  new TrieNode[26]
 			TrieNode[] nexts;
+			// pass end 不要！这题不需要！
+			// 有哪些字符串划过了这个节点，这些字符串的下标，记录！
 			ArrayList<Integer> indies;
 
 			public TrieNode() {
@@ -29,10 +32,12 @@ public class Code03_PrefixAndSuffixSearch {
 
 		TrieNode sufHead;
 
+		// 初始化，有所有的字符串！
 		public WordFilter(String[] words) {
 			preHead = new TrieNode();
 			sufHead = new TrieNode();
 			for (int i = 0; i < words.length; i++) {
+				// 所有字符串，i
 				String word = words[i];
 				TrieNode cur = preHead;
 				for (int j = 0; j < word.length(); j++) {
@@ -55,29 +60,31 @@ public class Code03_PrefixAndSuffixSearch {
 			}
 		}
 
+		// 给前缀 pref
+		// 给后缀 suff
 		public int f(String pref, String suff) {
 			ArrayList<Integer> preList = null;
 			TrieNode cur = preHead;
 			for (int i = 0; i < pref.length() && cur != null; i++) {
 				cur = cur.nexts[pref.charAt(i) - 'a'];
 			}
+			if(cur == null) {
+				return -1;
+			}
 			if (cur != null) {
 				preList = cur.indies;
 			}
-			if (preList == null) {
-				return -1;
-			}
 			ArrayList<Integer> sufList = null;
 			cur = sufHead;
 			for (int i = suff.length() - 1; i >= 0 && cur != null; i--) {
 				cur = cur.nexts[suff.charAt(i) - 'a'];
 			}
+			if(cur == null) {
+				return -1;
+			}
 			if (cur != null) {
 				sufList = cur.indies;
 			}
-			if (sufList == null) {
-				return -1;
-			}
 			ArrayList<Integer> small = preList.size() <= sufList.size() ? preList : sufList;
 			ArrayList<Integer> big = small == preList ? sufList : preList;
 			for (int i = small.size() - 1; i >= 0; i--) {
diff --git a/MCA算法突击课/第03期/mca_08/Code04_SameTeams.java b/MCA算法突击课/第03期/mca_08/Code04_SameTeams.java
index 5126ab5..156a391 100644
--- a/MCA算法突击课/第03期/mca_08/Code04_SameTeams.java
+++ b/MCA算法突击课/第03期/mca_08/Code04_SameTeams.java
@@ -29,6 +29,7 @@ public class Code04_SameTeams {
 		TrieNode root = new TrieNode();
 		TrieNode cur = null;
 		for (int i = 0; i < as.length; i++) {
+			// as[i] -> {4, 7, 3, 9}
 			cur = root;
 			for (int j = 1; j < as[i].length; j++) {
 				int diff = as[i][j] - as[i][j - 1];
@@ -41,6 +42,8 @@ public class Code04_SameTeams {
 		}
 		int[] ans = new int[bs.length];
 		for (int i = 0; i < bs.length; i++) {
+			// bs[i] = {4 5 9 3 2 ..}
+			// ans[i] = 0个
 			cur = root;
 			for (int j = 1; j < bs[i].length; j++) {
 				int diff = bs[i][j] - bs[i][j - 1];
diff --git a/MCA算法突击课/第03期/mca_08/Code05_MaximumFrequencyStack.java b/MCA算法突击课/第03期/mca_08/Code05_MaximumFrequencyStack.java
index 5cd1303..c2f84c9 100644
--- a/MCA算法突击课/第03期/mca_08/Code05_MaximumFrequencyStack.java
+++ b/MCA算法突击课/第03期/mca_08/Code05_MaximumFrequencyStack.java
@@ -17,14 +17,18 @@ public class Code05_MaximumFrequencyStack {
 		// 出现的最大次数
 		private int topTimes;
 		// 每层节点
-		private HashMap<Integer, ArrayList<Integer>> cntValues = new HashMap<>();
+		// HashMap -> ArrayList
+		private HashMap<Integer, ArrayList<Integer>>
+		cntValues = new HashMap<>();
+		
+		
 		// 每一个数出现了几次
 		private HashMap<Integer, Integer> valueTopTime = new HashMap<>();
 
 		public void push(int val) {
 			// 当前数词频+1
 			valueTopTime.put(val, valueTopTime.getOrDefault(val, 0) + 1);
-			// 当前数是什么词频 5 7次
+			// 当前数是什么词频
 			int curTopTimes = valueTopTime.get(val);
 			if (!cntValues.containsKey(curTopTimes)) {
 				cntValues.put(curTopTimes, new ArrayList<>());
diff --git a/MCA算法突击课/第03期/mca_08/Code06_InsertDeleteGetRandom.java b/MCA算法突击课/第03期/mca_08/Code06_InsertDeleteGetRandom.java
index fe3e4c0..4def3be 100644
--- a/MCA算法突击课/第03期/mca_08/Code06_InsertDeleteGetRandom.java
+++ b/MCA算法突击课/第03期/mca_08/Code06_InsertDeleteGetRandom.java
@@ -18,8 +18,11 @@ public class Code06_InsertDeleteGetRandom {
 
 	public class RandomizedSet {
 
+		// v -> i
 		private HashMap<Integer, Integer> keyIndexMap;
+		// i -> v
 		private HashMap<Integer, Integer> indexKeyMap;
+		// 几个数进来了
 		private int size;
 
 		public RandomizedSet() {
@@ -38,9 +41,15 @@ public class Code06_InsertDeleteGetRandom {
 		}
 
 		public boolean remove(int val) {
+			// 拿最后的位置，填上当前要删掉数字的，洞！
 			if (keyIndexMap.containsKey(val)) {
+				// 删掉 30   7
+				// size-1位置的数字，填洞
+				// 查出30在7位置
 				int deleteIndex = keyIndexMap.get(val);
+				// 最后位置是啥？size - 1
 				int lastIndex = --size;
+				// x   lastKey
 				int lastKey = indexKeyMap.get(lastIndex);
 				keyIndexMap.put(lastKey, deleteIndex);
 				indexKeyMap.put(deleteIndex, lastKey);
diff --git a/MCA算法突击课/第03期/mca_08/Test.java b/MCA算法突击课/第03期/mca_08/Test.java
new file mode 100644
index 0000000..1027ba2
--- /dev/null
+++ b/MCA算法突击课/第03期/mca_08/Test.java
@@ -0,0 +1,96 @@
+package 第03期.mca_08;
+
+public class Test {
+
+	class Trie {
+
+		class Node {
+			public int pass;
+			public int end;
+			public Node[] nexts;
+
+			public Node() {
+				pass = 0;
+				end = 0;
+				nexts = new Node[26];
+			}
+		}
+
+		private Node root;
+
+		public Trie() {
+			root = new Node();
+		}
+
+		// 在该结构里，加入str，一次
+		public void insert(String str) {
+			Node cur = root;
+			cur.pass++;
+			for (int i = 0; i < str.length(); i++) {
+				int path = str.charAt(i) - 'a';
+				if (cur.nexts[path] == null) {
+					cur.nexts[path] = new Node();
+				}
+				// 往下跳！
+				cur = cur.nexts[path];
+				cur.pass++;
+			}
+			cur.end++;
+		}
+
+		// 在该结构里，删掉str，一次
+		public void erase(String str) {
+			if (countWordsEqualTo(str) != 0) {
+				Node cur = root;
+				cur.pass--;
+				for (int i = 0; i < str.length(); i++) {
+					int path = str.charAt(i) - 'a';
+					Node next = cur.nexts[path];
+					if (next.pass == 1) {
+						cur.nexts[path] = null;
+						return;
+					} else {
+						cur = cur.nexts[path];
+					}
+					cur.pass--;
+				}
+				cur.end--;
+			}
+		}
+
+		// 给你一个字符串，str，查一下str出现了几次
+		public int countWordsEqualTo(String str) {
+			Node cur = root;
+			for (int i = 0; i < str.length(); i++) {
+				int path = str.charAt(i) - 'a';
+				if (cur.nexts[path] == null) {
+					return 0;
+				}
+				// 往下跳！
+				cur = cur.nexts[path];
+			}
+			return cur.end;
+		}
+
+		// 给你一个字符串，str，查一下有多少个字符串以str开头
+		public int countWordsStartingWith(String str) {
+			Node cur = root;
+			for (int i = 0; i < str.length(); i++) {
+				int path = str.charAt(i) - 'a';
+				if (cur.nexts[path] == null) {
+					return 0;
+				}
+				// 往下跳！
+				cur = cur.nexts[path];
+			}
+			return cur.pass;
+		}
+	}
+
+//	public static void main(String[] args) {
+//		char cur = 'z';
+//		int path = cur - 'a';
+//		System.out.println(path);
+//	}
+
+}
diff --git a/MCA算法突击课/第03期/ppt/key/第08节.key b/MCA算法突击课/第03期/ppt/key/第08节.key
new file mode 100644
index 0000000..6011cde
Binary files /dev/null and b/MCA算法突击课/第03期/ppt/key/第08节.key differ
diff --git a/MCA算法突击课/第03期/ppt/powerpoint/第08节.pptx b/MCA算法突击课/第03期/ppt/powerpoint/第08节.pptx
new file mode 100644
index 0000000..756cc7b
Binary files /dev/null and b/MCA算法突击课/第03期/ppt/powerpoint/第08节.pptx differ