add leetcode : offer-37-38-59.1-59.2

Author: CodeWater404

Algorithm/src/offer/_37SerializedBinaryTree.java

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+package offer;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-20-18:45
+ * @Function Description ：37.序列化二叉树
+ */
+public class _37SerializedBinaryTree {
+    public class Codec {
+        public String serialize(TreeNode root) {
+            if(root == null) return "[]";
+            StringBuilder res = new StringBuilder("[");
+            Queue<TreeNode> queue = new LinkedList<>() {{ add(root); }};
+            while(!queue.isEmpty()) {
+                TreeNode node = queue.poll();
+                if(node != null) {
+                    res.append(node.val + ",");
+                    queue.add(node.left);
+                    queue.add(node.right);
+                }
+                else res.append("null,");
+            }
+            res.deleteCharAt(res.length() - 1);
+            res.append("]");
+            return res.toString();
+        }
+
+        public TreeNode deserialize(String data) {
+            if(data.equals("[]")) return null;
+            String[] vals = data.substring(1, data.length() - 1).split(",");
+            TreeNode root = new TreeNode(Integer.parseInt(vals[0]));
+            Queue<TreeNode> queue = new LinkedList<>() {{ add(root); }};
+            int i = 1;
+            while(!queue.isEmpty()) {
+                TreeNode node = queue.poll();
+                if(!vals[i].equals("null")) {
+                    node.left = new TreeNode(Integer.parseInt(vals[i]));
+                    queue.add(node.left);
+                }
+                i++;
+                if(!vals[i].equals("null")) {
+                    node.right = new TreeNode(Integer.parseInt(vals[i]));
+                    queue.add(node.right);
+                }
+                i++;
+            }
+            return root;
+        }
+    }
+}

Algorithm/src/offer/_38ArrangementOfString.java

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+package offer;
+
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-20-18:46
+ * @Function Description ：38.字符串的排列
+ */
+public class _38ArrangementOfString {
+    class Solution {
+        List<String > res = new LinkedList<>();
+        char[] c;
+        public String[] permutation(String s) {
+            c = s.toCharArray();
+            dfs(0);
+            return res.toArray( new String[res.size()] );
+        }
+
+        public void dfs( int x ){
+            if ( x == c.length - 1){
+                res.add( String.valueOf(c));
+                return ;
+            }
+            HashSet<Character> set = new HashSet<>();
+            for( int i = x ; i < c.length ; i++ ){
+                if( set.contains(c[i]) ) continue;
+                set.add( c[i] );
+                // 将第i位字符固定在x位
+                swap( i , x );
+                dfs( x + 1 );
+                swap( i , x );
+            }
+        }
+
+        public void swap(int a , int b){
+            char temp = c[a];
+            c[a] = c[b];
+            c[b] = temp;
+        }
+    }
+}

Algorithm/src/offer/_59_1TheMaximumValueOfSlidingWindow.java

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+package offer;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-20-15:58
+ * @Function Description ：59.1滑动窗口的最大值
+ */
+public class _59_1TheMaximumValueOfSlidingWindow {
+    class Solution {
+
+        public int[] maxSlidingWindow(int[] nums, int k) {
+            int length = nums.length , hh = 0 , tt = -1 ;
+            // 虽然题目说数组不空，但是测试用例有。。。。。
+            if( length == 0 ) return new int[0];
+            // length - k + 1求得最大值个数
+            int[] q = new int[length] , res = new int[length - k + 1];
+
+            for( int i = 0 ; i < length ; i++ ){
+                if( hh <= tt && q[hh] < i - k + 1 )hh ++;
+                while( hh <= tt && nums[q[tt]] <= nums[i] ) tt--;
+                q[++tt] = i;
+                //  i - k + 1让res数组下标从0开始，不然开的数组会越界
+                if( i >= k - 1 ) res[i - k + 1] = nums[q[hh]]  ;
+            }
+
+            return res;
+        }
+    }
+}

Algorithm/src/offer/_59_2TheMaximumValueOfTheQueue.java

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+package offer;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+/**
+ * @author ： CodeWater
+ * @create ：2022-07-20-16:32
+ * @Function Description ：59.2 队列的最大值
+ */
+public class _59_2TheMaximumValueOfTheQueue {
+    class MaxQueue {
+
+        Deque<Integer> res , max ;
+        public MaxQueue() {
+            res = new LinkedList<>();
+            max = new LinkedList<>();
+        }
+
+        public int max_value() {
+            if( max.isEmpty() ) return -1;
+            return max.peekFirst();
+        }
+
+        public void push_back(int value) {
+            res.addLast( value );
+            while( !max.isEmpty() && max.peekLast() < value ) max.removeLast();
+            max.addLast(value);
+        }
+
+        public int pop_front() {
+            if( res.isEmpty() ) return -1;
+            int temp = res.pollFirst();
+            if( temp == max.peekFirst() ) max.removeFirst();
+            return temp;
+        }
+    }
+
+/**
+ * Your MaxQueue object will be instantiated and called as such:
+ * MaxQueue obj = new MaxQueue();
+ * int param_1 = obj.max_value();
+ * obj.push_back(value);
+ * int param_3 = obj.pop_front();
+ */
+}