modify code

MCA算法突击课/第03期/mca_05/Code01_BoatsToSavePeople.java

@@ -7,11 +7,11 @@ import java.util.Arrays;
 // 每艘船最多坐两人，且不能超过载重
 // 想让所有的人同时过河，并且用最好的分配方法让船尽量少
 // 返回最少的船数
-// 测试链接 : https://leetcode.com/problems/boats-to-save-people/
+// 测试链接 : https://leetcode.cn/problems/boats-to-save-people/
 public class Code01_BoatsToSavePeople {
 
 	// 首尾双指针的解法
-	public static int numRescueBoats2(int[] people, int limit) {
+	public static int numRescueBoats(int[] people, int limit) {
 		Arrays.sort(people);
 		int ans = 0;
 		int l = 0;

MCA算法突击课/第03期/mca_05/Code02_TrappingRainWater.java

@@ -5,6 +5,30 @@ package 第03期.mca_05;
 // 本题测试链接 : https://leetcode.cn/problems/trapping-rain-water/
 public class Code02_TrappingRainWater {
 
+	// 辅助数组的
+	public static int zuo(int[] arr) {
+		int n = arr.length;
+		if (n < 3) {
+			return 0;
+		}
+		int[] leftMax = new int[n];
+		leftMax[0] = arr[0];
+		for (int i = 1; i < n; i++) {
+			leftMax[i] = Math.max(leftMax[i - 1], arr[i]);
+		}
+		int[] rightMax = new int[n];
+		rightMax[n - 1] = arr[n - 1];
+		for (int i = n - 2; i >= 0; i--) {
+			rightMax[i] = Math.max(rightMax[i + 1], arr[i]);
+		}
+		int ans = 0;
+		for (int i = 1; i < n - 1; i++) {
+			ans += Math.max(Math.min(leftMax[i - 1], rightMax[i + 1]) - arr[i], 0);
+		}
+		return ans;
+	}
+
+	// 首尾双指针
 	public static int trap(int[] arr) {
 		if (arr == null || arr.length < 2) {
 			return 0;

MCA算法突击课/第03期/mca_05/Code03_LongestSumSubArrayLength.java

@@ -11,20 +11,51 @@ public class Code03_LongestSumSubArrayLength {
 		if (arr == null || arr.length == 0) {
 			return 0;
 		}
+		// key : 某个前缀和 value : 最早位置
 		HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
+		// 非常重要 !
 		map.put(0, -1);
-		int len = 0;
+		int ans = 0;
 		int sum = 0;
 		for (int i = 0; i < arr.length; i++) {
+			// sum : 0.....i 整体的和
 			sum += arr[i];
 			if (map.containsKey(sum - k)) {
-				len = Math.max(i - map.get(sum - k), len);
+				// 0.......730 1000 k = 100
+				// 0...17 900
+				// 18..730
+				// 长度 = i - 最早位置
+				ans = Math.max(i - map.get(sum - k), ans);
 			}
 			if (!map.containsKey(sum)) {
 				map.put(sum, i);
 			}
 		}
-		return len;
+		return ans;
+	}
+
+	public int maxSubArrayLen2(int[] arr, int k) {
+		if (arr == null || arr.length == 0) {
+			return 0;
+		}
+		// key : 某个前缀和 value : 最早位置
+		HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
+		int ans = 0;
+		int sum = 0;
+		for (int i = 0; i < arr.length; i++) {
+			sum += arr[i];
+			if (sum == k) {
+				ans = Math.max(i + 1, ans);
+			} else {
+				if (map.containsKey(sum - k)) {
+					ans = Math.max(i - map.get(sum - k), ans);
+				}
+			}
+			if (!map.containsKey(sum)) {
+				map.put(sum, i);
+			}
+		}
+		return ans;
 	}
 
 }

MCA算法突击课/第03期/mca_05/Code05_LRUCache.java

@@ -3,7 +3,7 @@ package 第03期.mca_05;
 import java.util.HashMap;
 
 // 测试链接 : https://leetcode.cn/problems/lru-cache/
-public class Code08_LRUCache {
+public class Code05_LRUCache {
 
 	// 提交以下这个类
 	public class LRUCache {
@@ -43,28 +43,28 @@ public class Code08_LRUCache {
 				}
 			}
 
-			public void moveNodeToTail(Node node) {
-				if (tail == node) {
+			public void moveNodeToTail(Node x) {
+				if (tail == x) {
 					return;
 				}
-				if (head == node) {
-					head = node.next;
+				if (head == x) { // x在头部
+					head = x.next;
 					head.last = null;
 				} else {
-					node.last.next = node.next;
-					node.next.last = node.last;
+					x.last.next = x.next;
+					x.next.last = x.last;
 				}
-				node.last = tail;
-				node.next = null;
-				this.tail.next = node;
-				this.tail = node;
+				x.last = tail;
+				x.next = null;
+				tail.next = x;
+				tail = x;
 			}
 
 			public Node removeHead() {
 				if (head == null) {
 					return null;
 				}
-				Node ans = this.head;
+				Node ans = head;
 				if (head == tail) {
 					head = null;
 					tail = null;
@@ -78,8 +78,11 @@ public class Code08_LRUCache {
 
 		}
 
+		//  A -> Node
 		private HashMap<Integer, Node> keyNodeMap;
+		// Node 串成的双向链表
 		private DoubleLinkedList nodeList;
+		// 这个结构的容量!
 		private final int capacity;
 
 		public LRUCache(int cap) {
@@ -97,12 +100,16 @@ public class Code08_LRUCache {
 			return -1;
 		}
 
+		// A 23
 		public void put(int key, int value) {
 			if (keyNodeMap.containsKey(key)) {
 				Node node = keyNodeMap.get(key);
 				node.val = value;
 				nodeList.moveNodeToTail(node);
 			} else {
+				// 之前没有A的记录，新增!
+				// 1) 结构满了
+				// 2) 结构没有满
 				if (keyNodeMap.size() == capacity) {
 					removeMostUnusedCache();
 				}

MCA算法突击课/第03期/mca_06/Code01_UnionFind.java

@@ -1,7 +1,7 @@
-package 第03期.mca_05;
+package 第03期.mca_06;
 
+// 并查集实现
 // 测试链接 : https://www.nowcoder.com/questionTerminal/e7ed657974934a30b2010046536a5372
-// 请务必理解这个文件的实现，而且还提供了测试链接
 // 提交如下的code，并把主类名改成"Main"
 // 在测试链接里可以直接通过
 // 请同学们务必参考如下代码中关于输入、输出的处理
@@ -13,7 +13,7 @@ import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
 import java.io.StreamTokenizer;
 
-public class Code05_UnionFind {
+public class Code01_UnionFind {
 
 	public static int MAXN = 1000001;
 

MCA算法突击课/第03期/mca_06/Code02_MostStonesRemovedWithSameRowOrColumn.java

@@ -1,4 +1,4 @@
-package 第03期.mca_05;
+package 第03期.mca_06;
 
 import java.util.HashMap;
 
@@ -9,7 +9,7 @@ import java.util.HashMap;
 // 其中 stones[i] = [xi, yi] 表示第 i 块石头的位置，
 // 返回 可以移除的石子 的最大数量。
 // 测试链接 : https://leetcode.cn/problems/most-stones-removed-with-same-row-or-column/
-public class Code06_MostStonesRemovedWithSameRowOrColumn {
+public class Code02_MostStonesRemovedWithSameRowOrColumn {
 
 	public static int removeStones(int[][] stones) {
 		int n = stones.length;

MCA算法突击课/第03期/mca_06/Code03_CouplesHoldingHands.java

@@ -1,4 +1,4 @@
-package 第03期.mca_05;
+package 第03期.mca_06;
 
 // n对情侣坐在连续排列的 2n 个座位上，想要牵到对方的手
 // 人和座位由一个整数数组 row 表示，其中 row[i] 是坐在第 i 个座位上的人的ID
@@ -6,7 +6,7 @@ package 第03期.mca_05;
 // 返回 最少交换座位的次数，以便每对情侣可以并肩坐在一起
 // 每次交换可选择任意两人，让他们站起来交换座位
 // 测试链接 : https://leetcode.cn/problems/couples-holding-hands/
-public class Code07_CouplesHoldingHands {
+public class Code03_CouplesHoldingHands {
 
 	public int minSwapsCouples(int[] row) {
 		int n = row.length;

MCA算法突击课/第03期/mca_06/Code04_TopologicalSort.java

@@ -0,0 +1,89 @@
+package 第03期.mca_06;
+
+// 根据入度来求拓扑排序，牛客网的测试数据
+// 测试链接 : https://www.nowcoder.com/questionTerminal/88f7e156ca7d43a1a535f619cd3f495c
+// 请同学们务必参考如下代码中关于输入、输出的处理
+// 这是输入输出处理效率很高的写法
+// 提交以下所有代码，把主类名改成Main，可以直接通过
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
+import java.io.StreamTokenizer;
+import java.util.ArrayList;
+import java.util.Arrays;
+
+public class Code04_TopologicalSort {
+
+	public static int MAXN = 200001;
+
+	public static int[] queue = new int[MAXN];
+
+	public static int[] indegree = new int[MAXN];
+
+	public static int[] ans = new int[MAXN];
+
+	public static int n, m, from, to;
+
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		StreamTokenizer in = new StreamTokenizer(br);
+		PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
+		while (in.nextToken() != StreamTokenizer.TT_EOF) {
+			n = (int) in.nval;
+			in.nextToken();
+			m = (int) in.nval;
+			ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
+			for (int i = 0; i <= n; i++) {
+				graph.add(new ArrayList<>());
+			}
+			for (int i = 0; i < m; i++) {
+				in.nextToken();
+				from = (int) in.nval;
+				in.nextToken();
+				to = (int) in.nval;
+				graph.get(from).add(to);
+			}
+			if (!topoSort(graph)) {
+				out.println(-1);
+			} else {
+				for (int i = 0; i < n - 1; i++) {
+					out.print(ans[i] + " ");
+				}
+				out.println(ans[n - 1]);
+			}
+			out.flush();
+		}
+	}
+
+	// 有拓扑排序返回true
+	// 没有拓扑排序返回false
+	public static boolean topoSort(ArrayList<ArrayList<Integer>> graph) {
+		Arrays.fill(indegree, 1, n + 1, 0);
+		for (ArrayList<Integer> nexts : graph) {
+			for (int next : nexts) {
+				indegree[next]++;
+			}
+		}
+		int l = 0;
+		int r = 0;
+		for (int i = 1; i <= n; i++) {
+			if (indegree[i] == 0) {
+				queue[r++] = i;
+			}
+		}
+		int cnt = 0;
+		while (l < r) {
+			int cur = queue[l++];
+			ans[cnt++] = cur;
+			for (int next : graph.get(cur)) {
+				if (--indegree[next] == 0) {
+					queue[r++] = next;
+				}
+			}
+		}
+		return cnt == n;
+	}
+
+}

MCA算法突击课/第03期/mca_06/Code05_Kruskal.java

@@ -0,0 +1,99 @@
+package 第03期.mca_06;
+
+// 课上没讲这个实现
+// 因为是一样的，都是用Kruskal算法实现最小生成树，只不过是牛客网的测试数据
+// 测试链接 : https://www.nowcoder.com/questionTerminal/c23eab7bb39748b6b224a8a3afbe396b
+// 请同学们务必参考如下代码中关于输入、输出的处理
+// 这是输入输出处理效率很高的写法
+// 提交以下所有代码，把主类名改成Main，可以直接通过
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
+import java.io.StreamTokenizer;
+import java.util.Arrays;
+
+public class Code05_Kruskal {
+
+	public static int MAXM = 100001;
+
+	public static int[][] edges = new int[MAXM][3];
+
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		StreamTokenizer in = new StreamTokenizer(br);
+		PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
+		while (in.nextToken() != StreamTokenizer.TT_EOF) {
+			int n = (int) in.nval;
+			in.nextToken();
+			int m = (int) in.nval;
+			for (int i = 0; i < m; i++) {
+				in.nextToken();
+				edges[i][0] = (int) in.nval;
+				in.nextToken();
+				edges[i][1] = (int) in.nval;
+				in.nextToken();
+				edges[i][2] = (int) in.nval;
+			}
+			Arrays.sort(edges, 0, m, (a, b) -> a[2] - b[2]);
+			build(n);
+			int ans = 0;
+			for (int[] edge : edges) {
+				if (union(edge[0], edge[1])) {
+					ans += edge[2];
+				}
+			}
+			out.println(ans);
+			out.flush();
+		}
+	}
+
+	// 下面是并查集结构
+	public static int MAXN = 10001;
+
+	public static int[] father = new int[MAXN];
+
+	public static int[] size = new int[MAXN];
+
+	public static int[] help = new int[MAXN];
+
+	public static void build(int n) {
+		for (int i = 1; i <= n; i++) {
+			father[i] = i;
+			size[i] = 1;
+		}
+	}
+
+	private static int find(int i) {
+		int size = 0;
+		while (i != father[i]) {
+			help[size++] = i;
+			i = father[i];
+		}
+		while (size > 0) {
+			father[help[--size]] = i;
+		}
+		return i;
+	}
+
+	// 如果i和j，原本是一个集合，返回false
+	// 如果i和j，不是一个集合，合并，然后返回true
+	public static boolean union(int i, int j) {
+		int fi = find(i);
+		int fj = find(j);
+		if (fi != fj) {
+			if (size[fi] >= size[fj]) {
+				father[fj] = fi;
+				size[fi] += size[fj];
+			} else {
+				father[fi] = fj;
+				size[fj] += size[fi];
+			}
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+}

MCA算法突击课/第03期/mca_06/Code06_OptimizeWaterDistributionInVillage.java

@@ -0,0 +1,90 @@
+package 第03期.mca_06;
+
+import java.util.Arrays;
+
+// 村里面一共有 n 栋房子
+// 我们希望通过建造水井和铺设管道来为所有房子供水。
+// 对于每个房子 i，我们有两种可选的供水方案：
+// 一种是直接在房子内建造水井，
+// 成本为 wells[i - 1](注意 -1 ，因为 索引从0开始)
+// 另一种是从另一口井铺设管道引水，
+// 数组 pipes 给出了在房子间铺设管道的成本
+// 其中每个 pipes[j] = [house1j, house2j, costj]
+// 代表用管道将 house1j 和 house2j连接在一起的成本
+// 连接是双向的
+// 请返回 为所有房子都供水的最低总成本
+// 测试链接 : https://leetcode.cn/problems/optimize-water-distribution-in-a-village/
+public class Code06_OptimizeWaterDistributionInVillage {
+
+	public static int MAXN = 10010;
+
+	public static int[][] edges = new int[MAXN << 1][3];
+
+	public static int esize;
+
+	public static int[] father = new int[MAXN];
+
+	public static int[] size = new int[MAXN];
+
+	public static int[] help = new int[MAXN];
+
+	public static void build(int n) {
+		for (int i = 0; i <= n; i++) {
+			father[i] = i;
+			size[i] = 1;
+		}
+	}
+
+	public static int find(int i) {
+		int s = 0;
+		while (i != father[i]) {
+			help[s++] = i;
+			i = father[i];
+		}
+		while (s > 0) {
+			father[help[--s]] = i;
+		}
+		return i;
+	}
+
+	public static boolean union(int i, int j) {
+		int f1 = find(i);
+		int f2 = find(j);
+		if (f1 != f2) {
+			if (size[f1] >= size[f2]) {
+				father[f2] = f1;
+				size[f1] += size[f2];
+			} else {
+				father[f1] = f2;
+				size[f2] += size[f1];
+			}
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+	public static int minCostToSupplyWater(int n, int[] wells, int[][] pipes) {
+		esize = 0;
+		for (int i = 0; i < n; i++, esize++) {
+			edges[esize][0] = 0;
+			edges[esize][1] = i + 1;
+			edges[esize][2] = wells[i];
+		}
+		for (int i = 0; i < pipes.length; i++, esize++) {
+			edges[esize][0] = pipes[i][0];
+			edges[esize][1] = pipes[i][1];
+			edges[esize][2] = pipes[i][2];
+		}
+		Arrays.sort(edges, 0, esize, (a, b) -> a[2] - b[2]);
+		build(n);
+		int ans = 0;
+		for (int i = 0; i < esize; i++) {
+			if (union(edges[i][0], edges[i][1])) {
+				ans += edges[i][2];
+			}
+		}
+		return ans;
+	}
+
+}

MCA算法突击课/第03期/mca_06/Code07_NetworkDelayTime.java

@@ -0,0 +1,41 @@
+package 第03期.mca_06;
+
+import java.util.ArrayList;
+import java.util.PriorityQueue;
+
+// Dijkstra算法
+// leetcode 743题，可以用这道题来练习Dijkstra算法
+// 测试链接 : https://leetcode.com/problems/network-delay-time
+public class Code07_NetworkDelayTime {
+
+	public static int networkDelayTime(int[][] times, int n, int k) {
+		ArrayList<ArrayList<int[]>> nexts = new ArrayList<>();
+		for (int i = 0; i <= n; i++) {
+			nexts.add(new ArrayList<>());
+		}
+		for (int[] delay : times) {
+			nexts.get(delay[0]).add(new int[] { delay[1], delay[2] });
+		}
+		PriorityQueue<int[]> heap = new PriorityQueue<>((a, b) -> a[1] - b[1]);
+		heap.add(new int[] { k, 0 });
+		boolean[] used = new boolean[n + 1];
+		int num = 0;
+		int max = 0;
+		while (!heap.isEmpty() && num < n) {
+			int[] record = heap.poll();
+			int cur = record[0];
+			int delay = record[1];
+			if (used[cur]) {
+				continue;
+			}
+			used[cur] = true;
+			num++;
+			max = Math.max(max, delay);
+			for (int[] next : nexts.get(cur)) {
+				heap.add(new int[] { next[0], delay + next[1] });
+			}
+		}
+		return num < n ? -1 : max;
+	}
+
+}