[IndexedTree] Indexed Tree example

Author: Seogeurim

src/IndexedTree/IndexedTreeTest.java

@@ -0,0 +1,97 @@
+package IndexedTree;
+
+import java.util.Arrays;
+
+public class IndexedTreeTest {
+
+    public static void main(String[] args) {
+        int[] inputs = {0, 3, 2, 4, 5, 1, 6, 2, 7};
+        // depth 3 => leaf 8개
+
+        IndexedTree it = new IndexedTree(inputs);
+        System.out.println(it);
+
+        it.makeTree(1, 1, it.leafSize);
+        System.out.println(it);
+
+        System.out.println(it.query(1, 1, it.leafSize, 3, 7));
+
+        // index 3을 4 -> 3으로 바꾸기
+        int targetIndex = 3;
+        int targetValue = 3;
+        int diff = targetValue - it.nums[targetIndex];
+        it.update(1, 1, it.leafSize, 3, diff);
+        it.nums[targetIndex] = targetValue;
+        System.out.println(it);
+    }
+}
+
+class IndexedTree {
+    int[] tree;
+    int[] nums;
+    int leafSize, depth;
+
+    public IndexedTree(int[] nums){
+        this.nums = nums;
+        this.depth = 0;
+        while (Math.pow(2, depth) < nums.length - 1) {
+            this.depth ++;
+        }
+        this.leafSize = (int) Math.pow(2, depth);
+        this.tree = new int[(int) Math.pow(2, depth + 1)];
+    }
+
+    // 내부 노드에 값을 채워준다.
+    public int makeTree(int node, int left, int right){
+        // leaf에 도달했을 때
+        if (left == right) {
+            if (left <= nums.length - 1) {
+                return tree[node] = nums[left];
+            } else {
+                return tree[node] = 0;
+            }
+        }
+        // 내부 노드일 경우
+        int mid = (left + right) / 2;
+        tree[node] = makeTree(node * 2, left, mid);
+        tree[node] += makeTree(node * 2 + 1, mid + 1, right);
+        return tree[node];
+    }
+
+    // 원하는 구간의 합 or 문제의 답을 구한다.
+    public int query(int node, int left, int right, int qLeft, int qRight){
+        if (qRight < left || qLeft > right){ // 관련이 없는 경우
+            return 0;
+        } else if (qLeft <= left && right <= qRight) { // 쿼리에 완전히 속하는 경우
+            return tree[node];
+        } else { // 그 외 : 애매하게 걸쳐있는 경우
+            int mid = (left + right) / 2;
+            return query(node * 2, left, mid, qLeft, qRight)
+                    + query(node * 2 + 1,mid + 1, right, qLeft, qRight);
+        }
+    }
+
+    // 특정값을 갱신한다.
+    public void update(int node, int left, int right, int index, int diff){
+        if (index < left || right < index) {
+            return;
+        } else {
+            tree[node] += diff;
+            if (left != right) {
+                int mid = (left + right) / 2;
+                update(node * 2, left, mid, index, diff);
+                update(node * 2 + 1, mid + 1, right, index, diff);
+            }
+        }
+    }
+
+    @Override
+    public String toString() {
+        return "IndexedTree{" +
+                "tree=" + Arrays.toString(tree) +
+                ", nums=" + Arrays.toString(nums) +
+                ", leafSize=" + leafSize +
+                ", depth=" + depth +
+                '}';
+    }
+}