Added MO's algorithm

Range queries/MO.cpp

@@ -0,0 +1,75 @@
+#include "bits/stdc++.h"
+using namespace std;
+const int N = 1e6+5;
+int a[N],bucket[N],cnt[N];
+int bucket_size;
+struct query{
+	int l,r,i;
+}q[N];
+int ans=0;
+
+void add(int index)
+{
+	cnt[a[index]]++;
+	if(cnt[a[index]] == 1)
+		ans++;
+}
+void remove(int index)
+{
+	cnt[a[index]]--;
+	if(cnt[a[index]] == 0)
+		ans--;
+}
+
+
+bool mycmp(query x, query y)
+{
+	if(x.l/bucket_size != y.l/bucket_size)
+		return x.l/bucket_size < y.l/bucket_size;
+	return x.r<y.r;
+}
+
+int main() {
+	int n,t,i,j,k=0;
+	scanf("%d",&n);
+	for(i=0;i<n;i++)
+		scanf("%d",&a[i]);					
+	bucket_size = ceil(sqrt(n));
+	scanf("%d",&t);
+	for(i=0;i<t;i++)
+	{
+		scanf("%d %d",&q[i].l,&q[i].r);
+		q[i].l--;	q[i].r--;
+		q[i].i = i;
+	}
+	sort(q,q+t,mycmp);
+	int left=0,right=0;
+	for(i=0;i<t;i++)
+	{
+		int L=q[i].l, R=q[i].r;
+		while(left < L)
+		{
+			remove(left);
+			left++;
+		}
+		while(left>L)
+		{
+			add(left-1);
+			left--;
+		}
+		while(right<=R)
+		{
+			add(right);
+			right++;
+		}
+		while(right>R+1)
+		{
+			remove(right-1);
+			right--;
+		}
+		bucket[q[i].i] = ans; 
+	}
+	for(i=0;i<t;i++)
+		printf("%d\n",bucket[i]);
+	return 0;
+}