Merge pull request chipbk10#109 from chipbk10/Tree

Solve Problem 315 - Count of smaller numbers after self

Author: chipbk10

src/tree/Problem315_CountOfSmallerNumbersAfterSelf.java

@@ -0,0 +1,49 @@
+package tree;
+
+import java.util.LinkedList;
+import java.util.List;
+
+public class Problem315_CountOfSmallerNumbersAfterSelf {
+
+
+    // TODO: still wrong
+    public List<Integer> countSmaller(int[] A) {
+        LinkedList<Integer> res = new LinkedList<>();
+        int n = A.length;
+        if (n == 0) return res;
+
+        TreeNode root = new TreeNode(A[n-1], 0);
+        for (int i = n-1; i >= 0; i--) {
+            res.addFirst(insert(root, A[i], 0));
+        }
+        return res;
+    }
+
+    private int insert(TreeNode node, int val, int smallers) {
+        if (node.val == val) return node.count + smallers;
+        if (node.val < val) {
+            if (node.right == null) {
+                node.right = new TreeNode(val, 0);
+                return node.count + smallers + 1;
+            }
+            return insert(node.right, val, node.count + smallers + 1);
+        }
+
+        node.count++;
+        if (node.left == null) {
+            node.left = new TreeNode(val, 0);
+            return smallers;
+        }
+
+        return insert(node.left, val, smallers);
+    }
+
+    class TreeNode {
+        int val, count;
+        TreeNode left, right;
+        public TreeNode(int val, int count) {
+            this.val = val;
+            this.count = count;
+        }
+    }
+}