modify code

src/class46/Code01_BurstBalloons.java

@@ -3,6 +3,43 @@ package class46;
 // 本题测试链接 : https://leetcode.com/problems/burst-balloons/
 public class Code01_BurstBalloons {
 
+	public static int maxCoins0(int[] arr) {
+		// [3,2,1,3]
+		// [1,3,2,1,3,1]
+		int N = arr.length;
+		int[] help = new int[N + 2];
+		for (int i = 0; i < N; i++) {
+			help[i + 1] = arr[i];
+		}
+		help[0] = 1;
+		help[N + 1] = 1;
+		return func(help, 1, N);
+	}
+
+	// L-1位置，和R+1位置，永远不越界，并且，[L-1] 和 [R+1] 一定没爆呢！
+	// 返回，arr[L...R]打爆所有气球，最大得分是什么
+	public static int func(int[] arr, int L, int R) {
+		if (L == R) {
+			return arr[L - 1] * arr[L] * arr[R + 1];
+		}
+		// 尝试每一种情况，最后打爆的气球，是什么位置
+		// L...R
+		// L位置的气球，最后打爆
+		int max = func(arr, L + 1, R) + arr[L - 1] * arr[L] * arr[R + 1];
+		// R位置的气球，最后打爆
+		max = Math.max(max, func(arr, L, R - 1) + arr[L - 1] * arr[R] * arr[R + 1]);
+		// 尝试所有L...R，中间的位置，(L,R)
+		for (int i = L + 1; i < R; i++) {
+			// i位置的气球，最后打爆
+			int left = func(arr, L, i - 1);
+			int right = func(arr, i + 1, R);
+			int last = arr[L - 1] * arr[i] * arr[R + 1];
+			int cur = left + right + last;
+			max = Math.max(max, cur);
+		}
+		return max;
+	}
+
 	public static int maxCoins1(int[] arr) {
 		if (arr == null || arr.length == 0) {
 			return 0;

src/class46/Code02_RemoveBoxes.java

@@ -3,6 +3,23 @@ package class46;
 // 本题测试链接 : https://leetcode.com/problems/remove-boxes/
 public class Code02_RemoveBoxes {
 
+	// arr[L...R]消除，而且前面跟着K个arr[L]这个数
+	// 返回：所有东西都消掉，最大得分
+	public static int func1(int[] arr, int L, int R, int K) {
+		if (L > R) {
+			return 0;
+		}
+		int ans = func1(arr, L + 1, R, 0) + (K + 1) * (K + 1);
+		
+		// 前面的K个X，和arr[L]数，合在一起了，现在有K+1个arr[L]位置的数
+		for (int i = L + 1; i <= R; i++) {
+			if (arr[i] == arr[L]) {
+				ans = Math.max(ans, func1(arr, L + 1, i - 1, 0) + func1(arr, i, R, K + 1));
+			}
+		}
+		return ans;
+	}
+
 	public static int removeBoxes1(int[] boxes) {
 		int N = boxes.length;
 		int[][][] dp = new int[N][N][N];
@@ -41,10 +58,15 @@ public class Code02_RemoveBoxes {
 		if (dp[L][R][K] > 0) {
 			return dp[L][R][K];
 		}
+		// 找到开头，
+		// 1,1,1,1,1,5
+		// 3 4 5 6 7 8
+		//         !
 		int last = L;
 		while (last + 1 <= R && boxes[last + 1] == boxes[L]) {
 			last++;
 		}
+		// K个1     (K + last - L) last
 		int pre = K + last - L;
 		int ans = (pre + 1) * (pre + 1) + process2(boxes, last + 1, R, 0, dp);
 		for (int i = last + 2; i <= R; i++) {

src/class46/Code03_DeleteAdjacentSameCharacter.java

@@ -59,6 +59,9 @@ public class Code03_DeleteAdjacentSameCharacter {
 		return process(str, 0, str.length - 1, false);
 	}
 
+	// str[L...R] 前面有没有跟着[L]字符，has T 有 F 无
+	// L,R,has
+	// 最少能剩多少字符，消不了
 	public static int process(char[] str, int L, int R, boolean has) {
 		if (L > R) {
 			return 0;
@@ -72,6 +75,7 @@ public class Code03_DeleteAdjacentSameCharacter {
 			K++;
 			index++;
 		}
+		// index表示，第一个不是[L]字符的位置
 		int way1 = (K > 1 ? 0 : 1) + process(str, index, R, false);
 		int way2 = Integer.MAX_VALUE;
 		for (int split = index; split <= R; split++) {

src/class46/HuffmanTree.java

@@ -0,0 +1,214 @@
+package class46;
+
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.Map.Entry;
+import java.util.PriorityQueue;
+
+// 本文件不牵扯任何byte类型的转化
+// 怎么转byte自己来，我只负责huffman算法本身的正确实现
+// 字符串为空的时候，自己处理边界吧
+// 实现的代码通过了大样本随机测试的对数器
+// 可以从main函数的内容开始看起
+public class HuffmanTree {
+
+	// 根据文章str, 生成词频统计表
+	public static HashMap<Character, Integer> countMap(String str) {
+		HashMap<Character, Integer> ans = new HashMap<>();
+		char[] s = str.toCharArray();
+		for (char cha : s) {
+			if (!ans.containsKey(cha)) {
+				ans.put(cha, 1);
+			} else {
+				ans.put(cha, ans.get(cha) + 1);
+			}
+		}
+		return ans;
+	}
+
+	public static class Node {
+		public int count;
+		public Node left;
+		public Node right;
+
+		public Node(int c) {
+			count = c;
+		}
+	}
+
+	public static class NodeComp implements Comparator<Node> {
+
+		@Override
+		public int compare(Node o1, Node o2) {
+			return o1.count - o2.count;
+		}
+
+	}
+
+	// 根据由文章生成词频表countMap，生成哈夫曼编码表
+	// key : 字符
+	// value: 该字符编码后的二进制形式
+	// 比如，频率表 A：60, B:45, C:13 D:69 E:14 F:5 G:3
+	// A 10
+	// B 01
+	// C 0011
+	// D 11
+	// E 000
+	// F 00101
+	// G 00100
+	public static HashMap<Character, String> huffmanForm(HashMap<Character, Integer> countMap) {
+		HashMap<Character, String> ans = new HashMap<>();
+		if (countMap.size() == 1) {
+			for (char key : countMap.keySet()) {
+				ans.put(key, "0");
+			}
+			return ans;
+		}
+		HashMap<Node, Character> nodes = new HashMap<>();
+		PriorityQueue<Node> heap = new PriorityQueue<>(new NodeComp());
+		for (Entry<Character, Integer> entry : countMap.entrySet()) {
+			Node cur = new Node(entry.getValue());
+			char cha = entry.getKey();
+			nodes.put(cur, cha);
+			heap.add(cur);
+		}
+		while (heap.size() != 1) {
+			Node a = heap.poll();
+			Node b = heap.poll();
+			Node h = new Node(a.count + b.count);
+			h.left = a;
+			h.right = b;
+			heap.add(h);
+		}
+		Node head = heap.poll();
+		fillForm(head, "", nodes, ans);
+		return ans;
+	}
+
+	public static void fillForm(Node head, String pre, HashMap<Node, Character> nodes, HashMap<Character, String> ans) {
+		if (nodes.containsKey(head)) {
+			ans.put(nodes.get(head), pre);
+		} else {
+			fillForm(head.left, pre + "0", nodes, ans);
+			fillForm(head.right, pre + "1", nodes, ans);
+		}
+	}
+
+	// 原始字符串str，根据哈夫曼编码表，转译成哈夫曼编码返回
+	public static String huffmanEncode(String str, HashMap<Character, String> huffmanForm) {
+		char[] s = str.toCharArray();
+		StringBuilder builder = new StringBuilder();
+		for (char cha : s) {
+			builder.append(huffmanForm.get(cha));
+		}
+		return builder.toString();
+	}
+
+	// 原始字符串的哈夫曼编码huffmanEncode，根据哈夫曼编码表，还原成原始字符串
+	public static String huffmanDecode(String huffmanEncode, HashMap<Character, String> huffmanForm) {
+		TrieNode root = createTrie(huffmanForm);
+		TrieNode cur = root;
+		char[] encode = huffmanEncode.toCharArray();
+		StringBuilder builder = new StringBuilder();
+		for (int i = 0; i < encode.length; i++) {
+			int index = encode[i] == '0' ? 0 : 1;
+			cur = cur.nexts[index];
+			if (cur.nexts[0] == null && cur.nexts[1] == null) {
+				builder.append(cur.value);
+				cur = root;
+			}
+		}
+		return builder.toString();
+	}
+
+	public static TrieNode createTrie(HashMap<Character, String> huffmanForm) {
+		TrieNode root = new TrieNode();
+		for (char key : huffmanForm.keySet()) {
+			char[] path = huffmanForm.get(key).toCharArray();
+			TrieNode cur = root;
+			for (int i = 0; i < path.length; i++) {
+				int index = path[i] == '0' ? 0 : 1;
+				if (cur.nexts[index] == null) {
+					cur.nexts[index] = new TrieNode();
+				}
+				cur = cur.nexts[index];
+			}
+			cur.value = key;
+		}
+		return root;
+	}
+
+	public static class TrieNode {
+		public char value;
+		public TrieNode[] nexts;
+
+		public TrieNode() {
+			value = 0;
+			nexts = new TrieNode[2];
+		}
+	}
+
+	// 为了测试
+	public static String randomNumberString(int len, int range) {
+		char[] str = new char[len];
+		for (int i = 0; i < len; i++) {
+			str[i] = (char) ((int) (Math.random() * range) + 'a');
+		}
+		return String.valueOf(str);
+	}
+
+	// 为了测试
+	public static void main(String[] args) {
+		// 根据词频表生成哈夫曼编码表
+		HashMap<Character, Integer> map = new HashMap<>();
+		map.put('A', 60);
+		map.put('B', 45);
+		map.put('C', 13);
+		map.put('D', 69);
+		map.put('E', 14);
+		map.put('F', 5);
+		map.put('G', 3);
+		HashMap<Character, String> huffmanForm = huffmanForm(map);
+		for (Entry<Character, String> entry : huffmanForm.entrySet()) {
+			System.out.println(entry.getKey() + " : " + entry.getValue());
+		}
+		System.out.println("====================");
+		// str是原始字符串
+		String str = "CBBBAABBACAABDDEFBA";
+		System.out.println(str);
+		// countMap是根据str建立的词频表
+		HashMap<Character, Integer> countMap = countMap(str);
+		// hf是根据countMap生成的哈夫曼编码表
+		HashMap<Character, String> hf = huffmanForm(countMap);
+		// huffmanEncode是原始字符串转译后的哈夫曼编码
+		String huffmanEncode = huffmanEncode(str, hf);
+		System.out.println(huffmanEncode);
+		// huffmanDecode是哈夫曼编码还原成的原始字符串
+		String huffmanDecode = huffmanDecode(huffmanEncode, hf);
+		System.out.println(huffmanDecode);
+		System.out.println("====================");
+		System.out.println("大样本随机测试开始");
+		// 字符串最大长度
+		int len = 500;
+		// 所含字符种类
+		int range = 26;
+		// 随机测试进行的次数
+		int testTime = 100000;
+		for (int i = 0; i < testTime; i++) {
+			int N = (int) (Math.random() * len) + 1;
+			String test = randomNumberString(N, range);
+			HashMap<Character, Integer> counts = countMap(test);
+			HashMap<Character, String> form = huffmanForm(counts);
+			String encode = huffmanEncode(test, form);
+			String decode = huffmanDecode(encode, form);
+			if (!test.equals(decode)) {
+				System.out.println(test);
+				System.out.println(encode);
+				System.out.println(decode);
+				System.out.println("出错了!");
+			}
+		}
+		System.out.println("大样本随机测试结束");
+	}
+
+}