fd

Author: liwentian

amazon/src/main/java/com/leetcode/amazon/Main.java

@@ -1,5 +1,7 @@
 package com.leetcode.amazon;
 
+import com.leetcode.library.TreeNode;
+
 import java.util.HashMap;
 import java.util.LinkedHashMap;
 
@@ -9,13 +11,43 @@
 
 public class Main {
 
-    public static void main(String[] args) {
-        HashMap<String, String> map = new HashMap<>();
-        map.put("one", "ones");
-        map.put("two", "twos");
+    public class LargestBSTSubtree {
+
+        class Result {
+            int count;
+            int lower;
+            int upper;
+
+            Result(int count, int lower, int upper) {
+                this.count = count;
+                this.lower = lower;
+                this.upper = upper;
+            }
+        }
+
+        public int largestBSTSubtree(TreeNode root) {
+            Result res = helper(root);
+            return Math.abs(res.count);
+        }
 
-        for (Integer key : map.keySet()) {
-            System.out.println(key);
+        private Result helper(TreeNode root) {
+            if (root == null) {
+                return new Result(0, Integer.MAX_VALUE, Integer.MIN_VALUE);
+            }
+
+            Result left = helper(root.left);
+            Result right = helper(root.right);
+
+            // 注意这里的等号千万别掉了，因为可能树中有节点相同
+            if (left.count < 0 || right.count < 0 || left.upper >= root.val || right.lower <= root.val) {
+                return new Result(-1 * Math.max(Math.abs(left.count), Math.abs(right.count)), 0, 0);
+            }
+
+            return new Result(left.count + right.count + 1, Math.min(left.lower, root.val), Math.max(right.upper, root.val));
         }
     }
+
+    public static void main(String[] args) {
+
+    }
 }

ebook/array/Array.tex

@@ -161,19 +161,21 @@ \subsubsection{Solution}
 
 \begin{Code}
 public boolean findTarget(TreeNode root, int k) {
-    HashSet<Integer> set = new HashSet<>();
-    return dfs(root, set, k);
+    List<Integer> nums = new ArrayList<>();
+    inorder(root, nums);
+    for (int i = 0, j = nums.size() - 1; i < j; ) {
+        if (nums.get(i) + nums.get(j) == k) return true;
+        if (nums.get(i) + nums.get(j) < k) i++;
+        else j--;
+    }
+    return false;
 }
 
-private boolean dfs(TreeNode node, HashSet<Integer> set, int k) {
-    if (node == null) {
-        return false;
-    }
-    if (set.contains(k - node.val)) {
-        return true;
-    }
-    set.add(node.val);
-    return dfs(node.left, set, k) || dfs(node.right, set, k);
+public void inorder(TreeNode root, List<Integer> nums) {
+    if (root == null) return;
+    inorder(root.left, nums);
+    nums.add(root.val);
+    inorder(root.right, nums);
 }
 \end{Code}
 

ebook/tree/Tree.tex

@@ -2734,9 +2734,11 @@ \subsubsection{Solution}
     }
 }
 
+int max = 0;
+
 public int largestBSTSubtree(TreeNode root) {
-    Result res = helper(root);
-    return Math.abs(res.count);
+    helper(root);
+    return max;
 }
 
 private Result helper(TreeNode root) {
@@ -2749,10 +2751,12 @@ \subsubsection{Solution}
 
     // 注意这里的等号千万别掉了，因为可能树中有节点相同
     if (left.count < 0 || right.count < 0 || left.upper >= root.val || right.lower <= root.val) {
-        return new Result(-1 * Math.max(Math.abs(left.count), Math.abs(right.count)), 0, 0);
+        return new Result(-1, 0, 0);
     }
 
-    return new Result(left.count + right.count + 1, Math.min(left.lower, root.val), Math.max(right.upper, root.val));
+    int size = left.count + 1 + right.count;
+    max = Math.max(size, max);
+    return new Result(size, Math.min(left.lower, root.val), Math.max(right.upper, root.val));
 }
 \end{Code}
 

solution/src/main/java/com/inuker/solution/LargestBSTSubtree.java

@@ -20,9 +20,11 @@ class Result {
         }
     }
 
+    int max = 0;
+
     public int largestBSTSubtree(TreeNode root) {
-        Result res = helper(root);
-        return Math.abs(res.count);
+        helper(root);
+        return max;
     }
 
     private Result helper(TreeNode root) {
@@ -35,9 +37,11 @@ private Result helper(TreeNode root) {
 
         // 注意这里的等号千万别掉了，因为可能树中有节点相同
         if (left.count < 0 || right.count < 0 || left.upper >= root.val || right.lower <= root.val) {
-            return new Result(-1 * Math.max(Math.abs(left.count), Math.abs(right.count)), 0, 0);
+            return new Result(-1, 0, 0);
         }
 
-        return new Result(left.count + right.count + 1, Math.min(left.lower, root.val), Math.max(right.upper, root.val));
+        int size = left.count + 1 + right.count;
+        max = Math.max(size, max);
+        return new Result(size, Math.min(left.lower, root.val), Math.max(right.upper, root.val));
     }
 }

solution/src/main/java/com/inuker/solution/TwoSumIV.java

@@ -2,7 +2,9 @@
 
 import com.leetcode.library.TreeNode;
 
+import java.util.ArrayList;
 import java.util.HashSet;
+import java.util.List;
 
 /**
  * Created by liwentian on 2017/9/10.
@@ -14,18 +16,20 @@
 public class TwoSumIV {
 
     public boolean findTarget(TreeNode root, int k) {
-        HashSet<Integer> set = new HashSet<>();
-        return dfs(root, set, k);
+        List<Integer> nums = new ArrayList<>();
+        inorder(root, nums);
+        for (int i = 0, j = nums.size() - 1; i < j; ) {
+            if (nums.get(i) + nums.get(j) == k) return true;
+            if (nums.get(i) + nums.get(j) < k) i++;
+            else j--;
+        }
+        return false;
     }
 
-    private boolean dfs(TreeNode node, HashSet<Integer> set, int k) {
-        if (node == null) {
-            return false;
-        }
-        if (set.contains(k - node.val)) {
-            return true;
-        }
-        set.add(node.val);
-        return dfs(node.left, set, k) || dfs(node.right, set, k);
+    public void inorder(TreeNode root, List<Integer> nums) {
+        if (root == null) return;
+        inorder(root.left, nums);
+        nums.add(root.val);
+        inorder(root.right, nums);
     }
 }