Update BIT - Binary Indexed Tree (Fenwick Tree).cpp

BIT - Binary Indexed Tree (Fenwick Tree).cpp

@@ -1,34 +1,3 @@
-1D BIT:
-
-int bit[N];
-
-void update(int idx, int val)
-{
-	while(idx<=n)
-	{
-		bit[idx]+=val;
-		idx+=idx&-idx;
-	}
-}
-
-int pref(int idx)
-{
-	int ans=0;
-	while(idx>0)
-	{
-		ans+=bit[idx];
-		idx-=idx&-idx;
-	}
-	return ans;
-}
-
-int rsum(int l, int r)
-{
-	return pref(r) - pref(l-1);
-}
-
-----------------------------------------------------------------------------------------------------------------------
-
 struct BIT
 {
 	int N;
@@ -49,15 +18,6 @@ struct BIT
 		}
 	}
 
-	void updateMax(int idx, int val)
-	{
-		while(idx <= N)
-		{
-			bit[idx] = max(bit[idx], val);
-			idx += idx & -idx;
-		}
-	}
-
 	int pref(int idx)
 	{
 		int ans = 0;
@@ -74,6 +34,31 @@ struct BIT
 		return pref(r) - pref(l - 1);
 	}
 
+	//returns first index such that pref[idx] >= val
+
+	int search(int val)
+	{
+		int curSum = 0, pos = 0;
+		for(int i = log2(N) + 1; i >= 0; i--)
+		{
+			if(pos + (1 << i) < N && curSum + bit[pos + (1 << i)] < val)
+			{
+				curSum += bit[pos + (1 << i)];
+				pos += (1 << i);
+			}
+		}
+		return pos + 1;
+	}
+
+	void updateMax(int idx, int val)
+	{
+		while(idx <= N)
+		{
+			bit[idx] = max(bit[idx], val);
+			idx += idx & -idx;
+		}
+	}
+
 	int prefMax(int idx)
 	{
 		int ans = -2e9;
@@ -86,37 +71,10 @@ struct BIT
 	}
 };
 
-Multiple BIT:
-
-int bit[2][N];
-
-void update(int i, int idx, int k)
-{
-	while(idx<=n)
-	{
-		bit[i][idx]+=k;
-		idx+=idx&-idx;
-	}
-}
-
-int pref(int i, int idx)
-{
-	int ans=0;
-	while(idx>0)
-	{
-		ans+=bit[i][idx];
-		idx-=idx&-idx;
-	}
-	return ans;
-}
-
-int rsum(int i, int l, int r)
-{
-	return pref(i, r) - pref(i, l-1);
-}
-
 //Problem 1: https://codeforces.com/contest/1073/problem/D
 //Solution 1: https://codeforces.com/contest/1073/submission/44863255
 
 //Problem 2: https://www.hackerrank.com/contests/university-codesprint-4/challenges/unique-art/problem
 //Solution 2: http://p.ip.fi/T9YM
+
+//Problem 3: https://csacademy.com/contest/round-47/task/cut-the-trees/statement/