1 files changed, 90 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/util/StringTrie.java b/src/main/java/com/google/devtools/build/lib/util/StringTrie.java
new file mode 100644
index 0000000000..4744c7e31f
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/util/StringTrie.java
@@ -0,0 +1,90 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.util;
+
+import com.google.common.base.Preconditions;
+
+
+/**
+ * A trie that operates on path segments of an input string instead of individual characters.
+ *
+ * <p>Only accepts strings that contain only low-ASCII characters (0-127)
+ *
+ * @param <T> the type of the values
+ */
+public class StringTrie<T> {
+  private static final int RANGE = 128;
+
+  @SuppressWarnings("unchecked")
+  private static class Node<T> {
+    private Node() {
+      children = new Node[RANGE];
+    }
+
+    private T value;
+    private Node<T> children[];
+  }
+
+  private final Node<T> root;
+
+  public StringTrie() {
+    root = new Node<T>();
+  }
+
+  /**
+   * Puts a value in the trie.
+   */
+  public void put(CharSequence key, T value) {
+    Node<T> current = root;
+
+    for (int i = 0; i < key.length(); i++) {
+      char ch = key.charAt(i);
+      Preconditions.checkState(ch < RANGE);
+      Node<T> next = current.children[ch];
+      if (next == null) {
+        next = new Node<T>();
+        current.children[ch] = next;
+      }
+
+      current = next;
+    }
+
+    current.value = value;
+  }
+
+  /**
+   * Gets a value from the trie. If there is an entry with the same key, that will be returned,
+   * otherwise, the value corresponding to the key that matches the longest prefix of the input.
+   */
+  public T get(String key) {
+    Node<T> current = root;
+    T lastValue = current.value;
+
+    for (int i = 0; i < key.length(); i++) {
+      char ch = key.charAt(i);
+      Preconditions.checkState(ch < RANGE);
+
+      current = current.children[ch];
+      if (current == null) {
+        break;
+      }
+
+      if (current.value != null) {
+        lastValue = current.value;
+      }
+    }
+
+    return lastValue;
+  }
+}