[LeetCode] Add January 29.

solved/LeetCode/Challenges/2020/January/29.kt

@@ -0,0 +1,22 @@
+class Solution {
+  data class Entry(val x: Int, val y: Int, val value: Int)
+
+  val entries = mutableListOf<Entry>()
+
+  fun verticalTraversal(root: TreeNode?): List<List<Int>> {
+      dfs(root, 0, 0)
+      entries.sortBy { it.x }
+      return entries.groupBy { it.x }.values
+        .map{ it.sortedWith(compareBy({-it.y}, {it.value})) }
+        .map { l -> l.map {it.value} }
+  }
+
+  fun dfs(root: TreeNode?, x: Int, y: Int) {
+    if (root == null) {
+      return
+    }
+    entries.add(Entry(x, y, root!!.`val`))
+    dfs(root!!.left, x - 1, y - 1)
+    dfs(root!!.right, x + 1, y - 1)
+  }
+}