Day 29 - Recursion III

RecursionIII.java

@@ -1,3 +1,4 @@
+import java.util.*;
 import utils.*;
 
 public class RecursionIII {
@@ -48,4 +49,170 @@ public int maxPathSumLeafToRoot(TreeNode root) {
         }
         return Math.max(left, right) + root.key;
     }
+
+    /**
+     * Binary Tree Path Sum To Target III
+     * <p>
+     * Given a binary tree in which each node contains an integer number. Determine
+     * if there exists a path (the path can only be from one node to itself or to
+     * any of its descendants), the sum of the numbers on the path is the given
+     * target number.
+     */
+    public boolean exist(TreeNode root, int target) {
+        this.map = new HashMap<>();
+        this.found = false;
+        map.put(0, 1);
+        exist(root, 0, target);
+        return this.found;
+    }
+
+    private boolean found;
+    private Map<Integer, Integer> map;
+
+    private void exist(TreeNode node, int sum, int target) {
+        if (found) {
+            return;
+        }
+        if (node == null) {
+            return;
+        }
+        int curSum = sum + node.key;
+        if (map.containsKey(curSum - target)) {
+            found = true;
+            return;
+        }
+
+        map.put(curSum, map.containsKey(curSum) ? map.get(curSum) + 1 : 1);
+        exist(node.left, curSum, target);
+        exist(node.right, curSum, target);
+
+        if (map.get(curSum) == 1) {
+            map.remove(curSum);
+        } else {
+            map.put(curSum, map.get(curSum) - 1);
+        }
+    }
+
+    /**
+     * Maximum Path Sum Binary Tree III
+     * <p>
+     * Given a binary tree in which each node contains an integer number. Find the
+     * maximum possible subpath sum(both the starting and ending node of the subpath
+     * should be on the same path from root to one of the leaf nodes, and the
+     * subpath is allowed to contain only one node).
+     */
+    public int maxPathSum2(TreeNode root) {
+        this.max = Integer.MIN_VALUE;
+        maxPathSum(root, 0);
+        return this.max;
+    }
+
+    private void maxPathSum(TreeNode node, int sum) {
+        if (node == null) {
+            return;
+        }
+
+        int curSum = sum + node.key;
+        this.max = Math.max(this.max, curSum);
+        curSum = Math.max(0, curSum);
+        maxPathSum(node.left, curSum);
+        maxPathSum(node.right, curSum);
+    }
+
+    /**
+     * Flatten Binary Tree to Linked List
+     * <p>
+     * Given a binary tree, flatten it to a linked list in-place.
+     */
+    public TreeNode flatten(TreeNode root) {
+        if (root == null) {
+            return root;
+        }
+        flattenHelper(root);
+        return root;
+    }
+
+    public TreeNode flattenHelper(TreeNode node) {
+        if (node.left == null && node.right == null) {
+            return node;
+        }
+
+        if (node.left == null) {
+            return flattenHelper(node.right);
+        }
+        if (node.right == null) {
+            node.right = node.left;
+            node.left = null;
+            return flattenHelper(node.right);
+        }
+
+        TreeNode left = flattenHelper(node.left);
+        TreeNode right = flattenHelper(node.right);
+        left.right = node.right;
+        node.right = node.left;
+        node.left = null;
+
+        return right;
+    }
+
+    public TreeNode reconstruct(int[] in, int[] pre) {
+        this.map = new HashMap<>();
+        for (int i = 0; i < in.length; i++) {
+            map.put(in[i], i);
+        }
+        TreeNode root = reconstruct(in, 0, in.length - 1, pre, 0, pre.length - 1);
+        return root;
+    }
+
+    private TreeNode reconstruct(int[] in, int inLeft, int inRight, int[] pre, int preLeft, int preRight) {
+        if (inLeft > inRight) {
+            return null;
+        }
+        TreeNode node = new TreeNode(pre[preLeft]);
+        int mid = map.get(pre[preLeft]);
+        node.left = reconstruct(in, inLeft, mid - 1, pre, preLeft + 1, preLeft + mid - inLeft);
+        node.right = reconstruct(in, mid + 1, inRight, pre, preRight + mid - inRight + 1, preRight);
+        return node;
+    }
+
+    public TreeNode reconstruct(int[] post) {
+        TreeNode root = reconstruct(post, 0, post.length - 1);
+        return root;
+    }
+
+    private TreeNode reconstruct(int[] post, int left, int right) {
+        if (right < left) {
+            return null;
+        }
+
+        TreeNode node = new TreeNode(post[right]);
+        if (left == right) {
+            return node;
+        }
+        int mid = binarySearch(post, left, right - 1, post[right]);
+        node.left = reconstruct(post, left, mid);
+        node.right = reconstruct(post, mid + 1, right - 1);
+        return node;
+
+    }
+
+    private int binarySearch(int[] post, int left, int right, int target) {
+        if (post[left] > target) {
+            return left - 1;
+        }
+        if (post[right] < target) {
+            return right;
+        }
+
+        while (left < right - 1) {
+            int mid = left + (right - left) / 2;
+            if (post[mid] < target) {
+                left = mid;
+            } else {
+                right = mid;
+            }
+        }
+
+        return left;
+    }
 }