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Commit 6cf7003

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easy ones
1 parent fc897a1 commit 6cf7003

12 files changed

+149
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lines changed

‎101_symmetric_tree.scala‎

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object Solution {
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def isSymmetric(root: TreeNode): Boolean = {
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if (root == null) true
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else isEqual(root.left, root.right)
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}
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def isEqual(left: TreeNode, right: TreeNode): Boolean = {
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if (left == null) right == null
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else if (right == null) left == null
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else (left.value == right.value) && isEqual(left.left, right.right) && isEqual(left.right, right.left)
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}
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}
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object Solution {
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def maxDepth(root: TreeNode): Int = {
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if (root == null) return 0
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else Math.max(1 + maxDepth(root.left), 1 + maxDepth(root.right))
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}
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}
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object Solution {
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def maxProfit(prices: Array[Int]): Int = {
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if (prices.isEmpty) 0
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else prices.scanLeft(prices.head)(Math.min(_, _)).tail zip prices map (x => x._2 - x._1) reduce(Math.max(_, _))
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}
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}

‎136_single_number.scala‎

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object Solution {
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def singleNumber(nums: Array[Int]): Int = {
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nums.reduce(_^_)
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}
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}

‎13_roman_to_integer.scala‎

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object Solution {
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def romanToInt(s: String): Int = {
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if (s == "") 0
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else s.head match {
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case 'V' => 5 + romanToInt(s.tail)
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case 'L' => 50 + romanToInt(s.tail)
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case 'D' => 500 + romanToInt(s.tail)
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case 'M' => 1000 + romanToInt(s.tail)
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case 'I' => if (s.tail == "") 1 else s.tail.head match {
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case 'V' => 4 + romanToInt(s.tail.tail)
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case 'X' => 9 + romanToInt(s.tail.tail)
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case _ => 1 + romanToInt(s.tail)
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}
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case 'X' => if (s.tail == "") 10 else s.tail.head match {
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case 'L' => 40 + romanToInt(s.tail.tail)
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case 'C' => 90 + romanToInt(s.tail.tail)
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case _ => 10 + romanToInt(s.tail)
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}
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case 'C' => if (s.tail == "") 100 else s.tail.head match {
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case 'D' => 400 + romanToInt(s.tail.tail)
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case 'M' => 900 + romanToInt(s.tail.tail)
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case _ => 100 + romanToInt(s.tail)
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}
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}
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}
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}

‎14_longest_common_prefix.scala‎

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object Solution {
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def longestCommonPrefix(strs: Array[String]): String = {
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if (strs.isEmpty) ""
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else{
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if (strs.map(_.isEmpty).reduce(_ || _)) ""
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else{
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val prefix = strs(0).head
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if (strs.map(_.head == prefix).reduce(_ && _)) prefix + longestCommonPrefix(strs.map(_.tail))
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else ""
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}
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}
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}
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}

‎20_valid_parentheses.scala‎

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object Solution {
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def isValid(s: String): Boolean = {
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return resolve(s, "s") == "s"
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}
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def resolve(s: String, stack: String): String = {
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if (s.isEmpty) stack
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else s.head match {
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case ')' => if (stack.last == '(') resolve(s.tail, stack.init) else "f"
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case ']' => if (stack.last == '[') resolve(s.tail, stack.init) else "f"
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case '}' => if (stack.last == '{') resolve(s.tail, stack.init) else "f"
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case c => resolve(s.tail, stack + c)
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}
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}
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}

‎21_merge_two_sorted_lists.scala‎

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object Solution {
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def mergeTwoLists(l1: ListNode, l2: ListNode): ListNode = {
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if (l1 == null) return l2
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else if (l2 == null) return l1
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else if(l1.x < l2.x) {
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val ret = new ListNode(l1.x)
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ret.next = mergeTwoLists(l1.next, l2)
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ret
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}else{
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val ret = new ListNode(l2.x)
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ret.next = mergeTwoLists(l1, l2.next)
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ret
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}
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}
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}

‎53_maximum_subarray.scala‎

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object Solution {
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def maxSubArray(nums: Array[Int]): Int = {
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val accSum = nums.toList.scanLeft(0)(_ + _).tail
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(accSum.scanLeft(0)(Math.min(_, _)).init zip accSum).map(x => x._2 - x._1).max
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}
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}

‎70_climbing_stairs.scala‎

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object Solution {
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val mat_mul = (x: (Int, Int, Int, Int), y: (Int, Int, Int, Int)) => (x._1 * y._1 + x._2 * y._3, x._1 * y._2 + x._2 * y._4, x._3 * y._1 + x._4 * y._3, x._3 * y._2 + x._4 * y._4)
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def fib_mat(n: Int): (Int, Int, Int, Int) = {
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if (n == 1) (1, 1, 1, 0)
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else if (n % 2 == 0) {
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val fib_half = fib_mat(n / 2)
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mat_mul(fib_half, fib_half)
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}else{
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val fib_half = fib_mat(n / 2)
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mat_mul(mat_mul(fib_half, fib_half), (1, 1, 1, 0))
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}
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}
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def climbStairs(n: Int): Int = {
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if (n == 1) 1
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else{
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val mat = fib_mat(n - 1)
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mat._1 + mat._2
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}
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}
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}

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