practice on 20190907

Author: fanzipei

108_convert_sorted_array_to_binary_search_tree.scala

@@ -0,0 +1,12 @@
+object Solution {
+    def sortedArrayToBST(nums: Array[Int]): TreeNode = {
+        if (nums.isEmpty) null
+        else{
+            val pivot = nums.length / 2
+            val root = new TreeNode(nums(pivot))
+            root.left = sortedArrayToBST(nums.slice(0, pivot))
+            root.right = sortedArrayToBST(nums.slice(pivot + 1, nums.length))
+            root
+        }
+    }
+}

543_diameter_of_binary_tree.scala

@@ -0,0 +1,16 @@
+object Solution {
+    
+    def maxDepth(root: TreeNode): (Int, Int) = {
+        if (root == null){
+            (0, 0)
+        }else{
+            val maxLeft = maxDepth(root.left)
+            val maxRight = maxDepth(root.right)
+            (Math.max(maxLeft._1 + 1, maxRight._1 + 1), Math.max(Math.max(maxLeft._2, maxRight._2), maxLeft._1 + maxRight._1))            
+        }
+    }
+    
+    def diameterOfBinaryTree(root: TreeNode): Int = {
+        maxDepth(root)._2
+    }
+}

79_word_search.scala

@@ -0,0 +1,24 @@
+object Solution {
+    
+    def existRest(board: Array[Array[Char]], word: String, lastLoc: (Int, Int), locSet: Set[(Int, Int)]): Boolean = {
+        if (word.isEmpty) true
+        else{
+            val candidates = Iterator(
+                (lastLoc._1 + 1, lastLoc._2),
+                (lastLoc._1 - 1, lastLoc._2),
+                (lastLoc._1, lastLoc._2 + 1),
+                (lastLoc._1, lastLoc._2 - 1)
+            ).filter(loc => (loc._1 >= 0 && loc._1 < board.length) && (loc._2 >= 0 && loc._2 < board(0).length) && (board(loc._1)(loc._2) == word.head) && !locSet.contains(loc))
+            if (candidates.isEmpty) false else candidates.exists(loc => existRest(board, word.tail, loc, locSet + loc))
+        }
+    }
+    
+    def exist(board: Array[Array[Char]], word: String): Boolean = {
+        val indices = for{
+            (a, i) <- board.iterator.zipWithIndex
+            (c, j) <- a.iterator.zipWithIndex
+            if( c == word.head )
+        } yield i -> j
+        if (indices.isEmpty) false else indices.exists(loc => existRest(board, word.tail, loc, Set(loc)))
+    }
+}