Merge pull request #157

add new problems 22.02

Author: Ashwagandha-coder

.idea/other.xml

@@ -1,7 +1,7 @@
 package com.github.contest
 
 
-import com.github.contest.heap.maxSubsequence
+import com.github.contest.binaryTree.recoverPreorderTraversal
 import java.util.TreeMap
 
 
@@ -11,7 +11,7 @@ import java.util.TreeMap
 
 fun main() {
 
-    maxSubsequence(intArrayOf(-1, -2, 3, 4), 3).apply { this.printArray() }
+    recoverPreorderTraversal("1-2--3--4-5--6--7")
 }
 
 fun generateTesting() {

contest/src/main/java/com/github/contest/Execute.kt

@@ -33,4 +33,38 @@ class FindElements(private val root: TreeNode?) {
         return false
     }
 
-}
+}
+
+/**
+ * 1028. Recover a Tree From Preorder Traversal
+ */
+
+fun recoverPreorderTraversal(traversal: String): TreeNode? {
+    val path = mutableListOf<TreeNode>()
+    var pos = 0
+    while (pos < traversal.length) {
+        var level = 0
+        while (traversal[pos] == '-') {
+            level++
+            pos++
+        }
+        var value = 0
+        while (pos < traversal.length && traversal[pos].isDigit()) {
+            value = value * 10 + (traversal[pos] - '0')
+            pos++
+        }
+        val node = TreeNode(value)
+        if (level == path.size) {
+            if (path.isNotEmpty()) {
+                path.last().left = node
+            }
+        } else {
+            while (level < path.size) {
+                path.removeLast()
+            }
+            path.last().right = node
+        }
+        path.add(node)
+    }
+    return path.firstOrNull()
+}

contest/src/main/java/com/github/contest/binaryTree/BinaryTreeLeetcode.kt

@@ -1,5 +1,7 @@
 package com.github.contest.graph
 
+import java.util.LinkedList
+
 /**
  * 997. Find the Town Judge
  */
@@ -16,4 +18,50 @@ fun findJudge(n: Int, trust: Array<IntArray>): Int {
         if (inEdges[person] == n - 1) return person
     }
     return -1
+}
+
+/**
+ * 1971. Find if Path Exists in Graph
+ */
+
+fun validPath(n: Int, edges: Array<IntArray>, source: Int, destination: Int): Boolean {
+    if (source == destination) return true
+    val adj = Array(n) { mutableListOf<Int>() }
+
+    for (edge in edges) {
+        adj[edge[0]].add(edge[1])
+        adj[edge[1]].add(edge[0])
+    }
+    val visited = BooleanArray(n) { false }
+    val queue = LinkedList<Int>()
+    queue.offer(source)
+    visited[source] = true
+
+    while (queue.isNotEmpty()) {
+        val vertex = queue.poll()
+        if (vertex == destination) return true
+
+        for (v in adj[vertex]) {
+            if (!visited[v]) {
+                visited[v] = true
+                queue.offer(v)
+            }
+        }
+    }
+
+    return false
+}
+
+/**
+ * 1791. Find Center of Star Graph
+ */
+
+fun findCenter(edges: Array<IntArray>): Int {
+    val (a, b) = edges[0]
+    val (c, d) = edges[1]
+
+    return when {
+        a == c || a == d -> a
+        else -> b
+    }
 }