Added solution to construct tree given cartesian traversal

YogenRaii · YogenRaii · commit 41c90a6fc53c · 2019-06-26T22:32:07.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/trees/CartesianTree.java b/src/main/java/com/eprogrammerz/examples/algorithm/trees/CartesianTree.java
@@ -0,0 +1,53 @@
+package com.eprogrammerz.examples.algorithm.trees;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class CartesianTree {
+    private class Node {
+        int val;
+        Node left;
+        Node right;
+        Node(int val) {
+            this.val = val;
+        }
+    }
+
+    Node buildTree(List<Integer> traversal) {
+        int rootIdx = findRootIdx(traversal);
+        if (rootIdx < 0 || rootIdx >= traversal.size()) {
+            return null;
+        }
+
+        Node root = new Node(traversal.get(rootIdx));
+        root.left = buildTree(traversal.subList(0, rootIdx));
+        root.right = buildTree(traversal.subList(rootIdx + 1, traversal.size()));
+        return root;
+    }
+
+    private int findRootIdx(List<Integer> traversal) {
+        int max = Integer.MIN_VALUE;
+        int idx = -1;
+        for (int i = 0; i < traversal.size(); i++) {
+            if (traversal.get(i) > max) {
+                max = traversal.get(i);
+                idx = i;
+            }
+        }
+        return idx;
+    }
+
+    @Test
+    public void testBuildTree() {
+        List<Integer> traversal = new ArrayList<>();
+        traversal.add(1);
+        traversal.add(3);
+        traversal.add(7);
+        traversal.add(5);
+        Node root = buildTree(traversal);
+        System.out.println(root);
+    }
+}
