msb_14613
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algorithm-class
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algorithmzuo 3 years ago
parent 55ddae77fc
commit 6a3cb5f17c
8 changed files with 98 additions and 245 deletions
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40
MCA算法突击课/第03期/mca_03/Code01_MergeKSortedLists.java
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@ -1,6 +1,5 @@
package 第03期.mca_03; package 第03期.mca_03;
import java.util.Comparator;
import java.util.PriorityQueue; import java.util.PriorityQueue;
// 给你一个链表数组，每个链表都已经按升序排列。 // 给你一个链表数组，每个链表都已经按升序排列。
@ -8,27 +7,48 @@ import java.util.PriorityQueue;
// 测试链接：https://leetcode.cn/problems/merge-k-sorted-lists/ // 测试链接：https://leetcode.cn/problems/merge-k-sorted-lists/
public class Code01_MergeKSortedLists { public class Code01_MergeKSortedLists {
// public static void main(String[] args) {
// ListNode h1 = new ListNode(1);
// h1.next = new ListNode(6);
// h1.next.next = new ListNode(9);
//
// ListNode h2 = new ListNode(3);
// h2.next = new ListNode(4);
// h2.next.next = new ListNode(4);
//
// ListNode h3 = new ListNode(5);
// h3.next = new ListNode(6);
// h3.next.next = new ListNode(9);
//
// ListNode[] arr = { h1, h2, h3 };
//
// ListNode all = mergeKLists(arr);
//
// while (all != null) {
// System.out.print(all.val + " ");
// all = all.next;
// }
// System.out.println();
// }
// 这个类不提交 // 这个类不提交
public static class ListNode { public static class ListNode {
public int val; public int val;
public ListNode next; public ListNode next;
}
// 提交以下方法
public static class ListNodeComparator implements Comparator<ListNode> {
@Override public ListNode(int v) {
public int compare(ListNode o1, ListNode o2) { val = v;
return o1.val - o2.val;
} }
} }
// 提交以下方法
public static ListNode mergeKLists(ListNode[] lists) { public static ListNode mergeKLists(ListNode[] lists) {
if (lists == null) { if (lists == null) {
return null; return null;
} }
PriorityQueue<ListNode> heap = new PriorityQueue<>(new ListNodeComparator()); // 小根堆！
PriorityQueue<ListNode> heap = new PriorityQueue<>((a, b) -> a.val - b.val);
// 所有链表的头节点，进入小根堆
for (int i = 0; i < lists.length; i++) { for (int i = 0; i < lists.length; i++) {
if (lists[i] != null) { if (lists[i] != null) {
heap.add(lists[i]); heap.add(lists[i]);

2
MCA算法突击课/第03期/mca_03/Code02_LevelTraversalBT.java
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@ -28,7 +28,9 @@ public class Code02_LevelTraversalBT {
Queue<TreeNode> queue = new LinkedList<>(); Queue<TreeNode> queue = new LinkedList<>();
queue.add(root); queue.add(root);
while (!queue.isEmpty()) { while (!queue.isEmpty()) {
// 当前轮做几次动作
int size = queue.size(); int size = queue.size();
// 当前层的链表
List<Integer> curLevel = new ArrayList<>(); List<Integer> curLevel = new ArrayList<>();
for (int i = 0; i < size; i++) { for (int i = 0; i < size; i++) {
TreeNode cur = queue.poll(); TreeNode cur = queue.poll();

35
MCA算法突击课/第03期/mca_03/Code03_ConstructBinaryTreeFromPreorderAndInorderTraversal.java
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@ -15,32 +15,43 @@ public class Code03_ConstructBinaryTreeFromPreorderAndInorderTraversal {
TreeNode left; TreeNode left;
TreeNode right; TreeNode right;
TreeNode(int val) { TreeNode(int v) {
this.val = val; val = v;
} }
} }
// 提交如下的方法 // 提交如下的方法
// pre和in真的是某棵二叉树的先序和中序数组
// 原始二叉树里，无重复值
public static TreeNode buildTree(int[] pre, int[] in) { public static TreeNode buildTree(int[] pre, int[] in) {
HashMap<Integer, Integer> valueIndexMap = new HashMap<>(); HashMap<Integer, Integer> valueIndexMap = new HashMap<>();
for (int i = 0; i < in.length; i++) { for (int i = 0; i < in.length; i++) {
valueIndexMap.put(in[i], i); valueIndexMap.put(in[i], i);
} }
return g(pre, 0, pre.length - 1, in, 0, in.length - 1, valueIndexMap); return process(pre, 0, pre.length - 1, in, 0, in.length - 1, valueIndexMap);
} }
public static TreeNode g(int[] pre, int L1, int R1, int[] in, int L2, int R2, // pre[pl....pr]
// in [il....ir]
// 子树！
public static TreeNode process(int[] pre, int pl, int pr, int[] in, int il, int ir,
HashMap<Integer, Integer> valueIndexMap) { HashMap<Integer, Integer> valueIndexMap) {
if (L1 > R1) { // pre[pl...pr]
return null; TreeNode head = new TreeNode(pre[pl]);
// [ 7 3 4 5 6 8 ]
// 4 5 6 7 8 9
//
// [ 3 4 7 6 5 8 ]
// 2 3 4 5 6 7
int headIndex = valueIndexMap.get(pre[pl]);
int leftSize = headIndex - il;
int rightSize = ir - headIndex;
if (leftSize > 0) {
head.left = process(pre, pl + 1, pl + leftSize, in, il, il + leftSize - 1, valueIndexMap);
} }
TreeNode head = new TreeNode(pre[L1]); if (rightSize > 0) {
if (L1 == R1) { head.right = process(pre, pr - rightSize + 1, pr, in, ir - rightSize + 1, ir, valueIndexMap);
return head;
} }
int find = valueIndexMap.get(pre[L1]);
head.left = g(pre, L1 + 1, L1 + find - L2, in, L2, find - 1, valueIndexMap);
head.right = g(pre, L1 + find - L2 + 1, R1, in, find + 1, R2, valueIndexMap);
return head; return head;
} }

27
MCA算法突击课/第03期/mca_03/Code04_IsCBT.java
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@ -1,6 +1,7 @@
package 第03期.mca_03; package 第03期.mca_03;
import java.util.LinkedList; import java.util.LinkedList;
import java.util.Queue;
// 给定一个二叉树的 root ，确定它是否是一个 完全二叉树 // 给定一个二叉树的 root ，确定它是否是一个 完全二叉树
// 在一个 完全二叉树 中，除了最后一个关卡外，所有关卡都是完全被填满的 // 在一个 完全二叉树 中，除了最后一个关卡外，所有关卡都是完全被填满的
@ -25,26 +26,24 @@ public class Code04_IsCBT {
if (head == null) { if (head == null) {
return true; return true;
} }
LinkedList<TreeNode> queue = new LinkedList<>(); Queue<TreeNode> queue = new LinkedList<>();
boolean leaf = false;
TreeNode l = null;
TreeNode r = null;
queue.add(head); queue.add(head);
// 一旦遇到不双全的节点，接下来遇到的所有节点都必须是叶！
boolean mustLeafStage = false;
while (!queue.isEmpty()) { while (!queue.isEmpty()) {
head = queue.poll(); TreeNode cur = queue.poll();
l = head.left; if ((cur.left == null && cur.right != null)
r = head.right; || (mustLeafStage && (cur.left != null || cur.right != null))) {
if ((leaf && (l != null || r != null)) || (l == null && r != null)) {
return false; return false;
} }
if (l != null) { if(cur.left == null || cur.right == null) {
queue.add(l); mustLeafStage = true;
} }
if (r != null) { if (cur.left != null) {
queue.add(r); queue.add(cur.left);
} }
if (l == null || r == null) { if (cur.right != null) {
leaf = true; queue.add(cur.right);
} }
} }
return true; return true;

54
MCA算法突击课/第03期/mca_03/Code05_IsBST.java
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@ -20,13 +20,6 @@ public class Code05_IsBST {
} }
// 提交以下的方法 // 提交以下的方法
public boolean isValidBST(TreeNode root) {
if (root == null) {
return true;
}
return process(root).isBST;
}
public static class Info { public static class Info {
public boolean isBST; public boolean isBST;
public int min; public int min;
@ -39,28 +32,41 @@ public class Code05_IsBST {
} }
} }
public static Info process(TreeNode root) { public boolean isValidBST(TreeNode root) {
if (root == null) { if (root == null) {
return true;
}
return process(root).isBST;
}
public static Info process(TreeNode x) {
if (x == null) {
return null; return null;
} }
Info left = process(root.left); Info leftInfo = process(x.left);
Info right = process(root.right); Info rightInfo = process(x.right);
int min = root.val; int min = x.val;
int max = root.val; int max = x.val;
if (leftInfo != null) {
min = Math.min(leftInfo.min, min);
max = Math.max(leftInfo.max, max);
}
if (rightInfo != null) {
min = Math.min(rightInfo.min, min);
max = Math.max(rightInfo.max, max);
}
boolean isBST = true; boolean isBST = true;
if (left != null) { if (leftInfo != null && !leftInfo.isBST) {
min = Math.min(min, left.min); isBST = false;
max = Math.max(max, left.max); }
if (!left.isBST || left.max >= root.val) { if (rightInfo != null && !rightInfo.isBST) {
isBST = false; isBST = false;
} }
if (leftInfo != null && leftInfo.max >= x.val) {
isBST = false;
} }
if (right != null) { if (rightInfo != null && rightInfo.min <= x.val) {
min = Math.min(min, right.min); isBST = false;
max = Math.max(max, right.max);
if (!right.isBST || root.val >= right.min) {
isBST = false;
}
} }
return new Info(isBST, min, max); return new Info(isBST, min, max);
} }

50
MCA算法突击课/第03期/mca_03/Code07_CompleteTreeNodeNumber.java
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@ -1,50 +0,0 @@
package 第03期.mca_03;
// 给你一棵 完全二叉树 的根节点 root ，求出该树的节点个数
// 完全二叉树 的定义如下：在完全二叉树中，除了最底层节点可能没填满外
// 其余每层节点数都达到最大值
// 并且最下面一层的节点都集中在该层最左边的若干位置
// 若最底层为第 h 层，则该层包含 1~ 2h 个节点。
// 测试链接 : https://leetcode.cn/problems/count-complete-tree-nodes/
public class Code07_CompleteTreeNodeNumber {
// 提交时不要提交这个类
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
}
// 提交如下的方法
public static int countNodes(TreeNode head) {
if (head == null) {
return 0;
}
return bs(head, 1, mostLeftLevel(head, 1));
}
// 当前来到node节点，node节点在level层，总层数是h
// 返回node为头的子树(必是完全二叉树)，有多少个节点
public static int bs(TreeNode node, int Level, int h) {
if (Level == h) {
return 1;
}
if (mostLeftLevel(node.right, Level + 1) == h) {
return (1 << (h - Level)) + bs(node.right, Level + 1, h);
} else {
return (1 << (h - Level - 1)) + bs(node.left, Level + 1, h);
}
}
// 如果node在第level层，
// 求以node为头的子树，最大深度是多少
// node为头的子树，一定是完全二叉树
public static int mostLeftLevel(TreeNode node, int level) {
while (node != null) {
level++;
node = node.left;
}
return level - 1;
}
}

48
MCA算法突击课/第03期/mca_03/Code08_DiameterOfBinaryTree.java
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@ -1,48 +0,0 @@
package 第03期.mca_03;
// 给定一棵二叉树，你需要计算它的直径长度
// 一棵二叉树的直径长度是任意两个结点路径长度中的最大值
// 这条路径可能穿过也可能不穿过根结点
// 测试链接 : https://leetcode.cn/problems/diameter-of-binary-tree/
public class Code08_DiameterOfBinaryTree {
// 提交时不要提交这个类
public static class TreeNode {
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int value) {
val = value;
}
}
// 提交以下的方法
public static int diameterOfBinaryTree(TreeNode root) {
return process(root).maxDistance;
}
public static class Info {
public int maxDistance;
public int height;
public Info(int m, int h) {
maxDistance = m;
height = h;
}
}
public static Info process(TreeNode x) {
if (x == null) {
return new Info(0, 0);
}
Info leftInfo = process(x.left);
Info rightInfo = process(x.right);
int height = Math.max(leftInfo.height, rightInfo.height) + 1;
int p1 = Math.max(leftInfo.maxDistance, rightInfo.maxDistance);
int p2 = leftInfo.height + rightInfo.height;
int maxDistance = Math.max(p1, p2);
return new Info(maxDistance, height);
}
}

87
MCA算法突击课/第03期/mca_03/Code09_MaxSubBSTSize.java
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@ -1,87 +0,0 @@
package 第03期.mca_03;
// 给定一个二叉树，找到其中最大的二叉搜索树（BST）子树，并返回该子树的大小
// 其中，最大指的是子树节点数最多的
// 二叉搜索树（BST）中的所有节点都具备以下属性：
// 左子树的值小于其父（根）节点的值
// 右子树的值大于其父（根）节点的值
// 注意：子树必须包含其所有后代
// 测试链接 : https://leetcode.cn/problems/largest-bst-subtree
public class Code09_MaxSubBSTSize {
// 提交时不要提交这个类
public static class TreeNode {
public int val;
public TreeNode left;
public TreeNode right;
public TreeNode(int value) {
val = value;
}
}
// 提交如下方法
public static int largestBSTSubtree(TreeNode head) {
if (head == null) {
return 0;
}
return process(head).maxBSTSubtreeSize;
}
public static class Info {
public int maxBSTSubtreeSize;
public int allSize;
public int max;
public int min;
public Info(int m, int a, int ma, int mi) {
maxBSTSubtreeSize = m;
allSize = a;
max = ma;
min = mi;
}
}
public static Info process(TreeNode x) {
if (x == null) {
return null;
}
Info leftInfo = process(x.left);
Info rightInfo = process(x.right);
int max = x.val;
int min = x.val;
int allSize = 1;
if (leftInfo != null) {
max = Math.max(leftInfo.max, max);
min = Math.min(leftInfo.min, min);
allSize += leftInfo.allSize;
}
if (rightInfo != null) {
max = Math.max(rightInfo.max, max);
min = Math.min(rightInfo.min, min);
allSize += rightInfo.allSize;
}
int p1 = -1;
if (leftInfo != null) {
p1 = leftInfo.maxBSTSubtreeSize;
}
int p2 = -1;
if (rightInfo != null) {
p2 = rightInfo.maxBSTSubtreeSize;
}
int p3 = -1;
boolean leftBST = leftInfo == null ? true : (leftInfo.maxBSTSubtreeSize == leftInfo.allSize);
boolean rightBST = rightInfo == null ? true : (rightInfo.maxBSTSubtreeSize == rightInfo.allSize);
if (leftBST && rightBST) {
boolean leftMaxLessX = leftInfo == null ? true : (leftInfo.max < x.val);
boolean rightMinMoreX = rightInfo == null ? true : (x.val < rightInfo.min);
if (leftMaxLessX && rightMinMoreX) {
int leftSize = leftInfo == null ? 0 : leftInfo.allSize;
int rightSize = rightInfo == null ? 0 : rightInfo.allSize;
p3 = leftSize + rightSize + 1;
}
}
return new Info(Math.max(p1, Math.max(p2, p3)), allSize, max, min);
}
}
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