Create BinaryIndexedTree.java

Author: peijunz

BinaryIndexedTree.java

@@ -0,0 +1,28 @@
+class BinaryIndexedTree {
+    int[] tree;
+
+    static int lowbit(int x) {
+        return x & -x;
+    }
+    public BinaryIndexedTree(int[] nums) {
+        tree = new int[nums.length+1];
+        for (int i = 0; i < nums.length; i++)
+            add(i, nums[i]);
+    }
+    public int query(int x) { // sum(nums[:x])
+        int ans = 0;
+        for (int i = x; i > 0; i -= lowbit(i))
+            ans += tree[i];
+        return ans;
+    }
+    public void add(int x, int u) { // nums[x] += u
+        for (int i = x+1; i < tree.length; i += lowbit(i))
+            tree[i] += u;
+    }
+    public void set(int x, int y) { // nums[x] = y
+        add(x, y - query(x+1) + query(x));
+    }
+    public int sumRange(int l, int r) {
+        return query(r+1) - query(l);
+    }
+}