diff --git a/Leecode/src/main/java/com/markilue/leecode/hot100/second/T46_105_BuildTree.java b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T46_105_BuildTree.java index 5d244c5..27ff715 100644 --- a/Leecode/src/main/java/com/markilue/leecode/hot100/second/T46_105_BuildTree.java +++ b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T46_105_BuildTree.java @@ -146,11 +146,11 @@ public class T46_105_BuildTree { //尝试官方最快:本质上就是逐步推进来确定边界，不用挨个寻找 public TreeNode buildTree5(int[] preorder, int[] inorder) { - return build1(preorder,inorder,Integer.MIN_VALUE);//找一个一定不会相等的即可 + return build1(preorder, inorder, Integer.MIN_VALUE);//找一个一定不会相等的即可 } public TreeNode build1(int[] preorder, int[] inorder, int stop) {//只确定右边界 - if (pre > preorder.length) { + if (pre >= preorder.length) { return null; } if (inorder[in] == stop) {//遍历到了右边界 @@ -164,4 +164,27 @@ public class T46_105_BuildTree { } + int in1 = 0; + int pre1 = 0; + + public TreeNode buildTree6(int[] preorder, int[] inorder) { + return buildChild(preorder, inorder, Integer.MIN_VALUE); + } + + public TreeNode buildChild(int[] preorder, int[] inorder, int stop) { + if (pre1 > preorder.length) { + return null; + } + if (inorder[in1] == stop) { + in1++; + return null; + } + TreeNode node = new TreeNode(preorder[pre1++]); + + node.left = buildChild(preorder, inorder, node.val); + node.right = buildChild(preorder, inorder, stop); + return node; + } + + } diff --git a/Leecode/src/main/java/com/markilue/leecode/hot100/second/T57_142_MaxProduct.java b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T57_152_MaxProduct.java similarity index 71% rename from Leecode/src/main/java/com/markilue/leecode/hot100/second/T57_142_MaxProduct.java rename to Leecode/src/main/java/com/markilue/leecode/hot100/second/T57_152_MaxProduct.java index 6c7072f..8fa4207 100644 --- a/Leecode/src/main/java/com/markilue/leecode/hot100/second/T57_142_MaxProduct.java +++ b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T57_152_MaxProduct.java @@ -10,7 +10,7 @@ import org.junit.Test; *@Description: TODO 力扣152 乘积最大子数组 *@Version: 1.0 */ -public class T57_142_MaxProduct { +public class T57_152_MaxProduct { @Test public void test() { @@ -69,12 +69,28 @@ public class T57_142_MaxProduct { dp[0][1] = nums[0];//要当前的最大值 :因为是子数组,必须要当前 for (int i = 1; i < nums.length; i++) { - dp[i][0] = Math.min(Math.min(nums[i], dp[i-1][0] * nums[i]), dp[i-1][1] * nums[i]); - dp[i][1] = Math.max(Math.max(nums[i], dp[i-1][0] * nums[i]), dp[i-1][1] * nums[i]);//因为如果当前为负数，最大值也可以变最小值；最小值也可以变最大值 + dp[i][0] = Math.min(Math.min(nums[i], dp[i - 1][0] * nums[i]), dp[i - 1][1] * nums[i]); + dp[i][1] = Math.max(Math.max(nums[i], dp[i - 1][0] * nums[i]), dp[i - 1][1] * nums[i]);//因为如果当前为负数，最大值也可以变最小值；最小值也可以变最大值 if (result < dp[i][1]) result = dp[i][1]; } return result; } + + public int maxProduct3(int[] nums) { + int max = nums[0]; + int min = nums[0]; + int resultMax = nums[0]; + + //每一个位置都是表示要当前值的最大值,因为要求子数组,如果不要就没办法计算了 + for (int i = 1; i < nums.length; i++) { + int temp = max; + max = Math.max(Math.max(nums[i], nums[i] * max), nums[i] * min); + min = Math.min(Math.min(nums[i], nums[i] * temp), nums[i] * min); + if (resultMax < max) resultMax = max; + } + + return resultMax; + } } diff --git a/Leecode/src/main/java/com/markilue/leecode/hot100/second/T64_207_CanFinish.java b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T64_207_CanFinish.java index d1ad5f9..e7f3f0b 100644 --- a/Leecode/src/main/java/com/markilue/leecode/hot100/second/T64_207_CanFinish.java +++ b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T64_207_CanFinish.java @@ -40,7 +40,7 @@ public class T64_207_CanFinish { } boolean[] used = new boolean[numCourses]; for (int i = 0; i < edge.size(); i++) { - if(!used[i]){ + if (!used[i]) { if (!dfs(i, used)) { return false; } @@ -73,6 +73,7 @@ public class T64_207_CanFinish { } boolean valid = true; + //本质上就是图的深度优先搜索:检测这个图是否存在环路 public boolean canFinish1(int numCourses, int[][] prerequisites) { edge = new ArrayList<>(); @@ -85,7 +86,7 @@ public class T64_207_CanFinish { } int[] visited = new int[numCourses]; - for (int i = 0; i < edge.size()&&valid; i++) { + for (int i = 0; i < edge.size() && valid; i++) { if (visited[i] == 0) { //从来没有遍历过 dfs(i, visited); @@ -115,4 +116,48 @@ public class T64_207_CanFinish { visited[start] = 2;//全都检查完了,没有问题 } + public boolean canFinish2(int numCourses, int[][] prerequisites) { + + //遍历prerequisites确定每个节点的子节点 + edge = new ArrayList<>(); + + for (int i = 0; i < numCourses; i++) { + edge.add(new ArrayList<>()); + } + + for (int[] prerequisite : prerequisites) { + edge.get(prerequisite[0]).add(prerequisite[1]); + } + + //挨个遍历所有的节点,判断是否会形成环路 + int[] visited = new int[numCourses]; + for (int i = 0; i < edge.size() && valid; i++) { + if (visited[i] == 0) { + //从来没有遍历过 + dfs1(i, visited); + } + } + return valid; + } + + public void dfs1(int start, int[] visited) { + visited[start] = 1;//正在遍历该节点 + List children = edge.get(start); + for (Integer child : children) { + if(visited[child]==0){ + //继续遍历,判断是否可以 + dfs1(child,visited); + if(!valid){ + return;//找到环路,不在进行遍历 + } + }else if(visited[child]==1){ + //找到环路,不在进行遍历 + valid=false; + return; + } + } + visited[start]=2;//遍历完成 + + } + } diff --git a/Leecode/src/main/java/com/markilue/leecode/hot100/second/T65_208_Trie.java b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T65_208_Trie.java new file mode 100644 index 0000000..83a6011 --- /dev/null +++ b/Leecode/src/main/java/com/markilue/leecode/hot100/second/T65_208_Trie.java @@ -0,0 +1,65 @@ +package com.markilue.leecode.hot100.second; + +import com.markilue.leecode.tree.TreeNode; + +import java.util.*; + +/** + *@BelongsProject: Leecode + *@BelongsPackage: com.markilue.leecode.hot100.second + *@Author: markilue + *@CreateTime: 2023-05-23 10:54 + *@Description: TODO 力扣208 实现Trie(前缀树) + *@Version: 1.0 + */ +public class T65_208_Trie { + + private T65_208_Trie[] children; + boolean isEnd; + + + public T65_208_Trie() { + children = new T65_208_Trie[26]; + isEnd = false; + } + + public void insert(String word) { + //挨个遍历插入 + T65_208_Trie node = this; + for (int i = 0; i < word.length(); i++) { + char value = word.charAt(i); + int index = value - 'a'; + if (node.children[index] == null) { + node.children[index] = new T65_208_Trie(); + } + node = node.children[index];//寻找他的下一个 + } + node.isEnd = true;//遍历到了最后 + } + + + public boolean search(String word) { + T65_208_Trie node = searchPrefix(word); + return node != null && node.isEnd; + } + + public boolean startsWith(String prefix) { + T65_208_Trie node = searchPrefix(prefix); + return node != null; + } + + public T65_208_Trie searchPrefix(String word) { + T65_208_Trie node = this; + + for (int j = 0; j < word.length(); j++) { + char c = word.charAt(j); + int index = c - 'a'; + if (node.children[index] == null) { + return null;//没有找到 + } + node = node.children[index]; + } + return node; + } + +}