Added Mo's Algorithm and Sqrt-Decomposition Folder

Square Root Decomposition/MO's Algorithm/MOAlgo.cpp

@@ -0,0 +1,85 @@
+//Problem : http://www.spoj.com/problems/DQUERY/
+//Time Complexity : O((n+q)*sqrt(n))
+
+#include <bits/stdc++.h>
+
+#define ll long long int
+#define mod 1000000007
+#define show(a) for(i=0;i<a.size();i++) cout<<a[i]<<" ";
+#define fi first
+#define se second
+#define vi vector<int>
+#define vs vector<string>
+#define vll vector<long long int>
+#define pb push_back
+#define pi pair<int,int>
+#define si set<int>
+#define sll set<ll>
+#define maxheap priority_queue<int>
+#define minheap priority_queue<int,vector<int>,greater<int>>
+#define mp make_pair
+#define fast_io() cin.sync_with_stdio(false);cout.sync_with_stdio(false);
+#define long_zero 0ll
+#define long_one 1ll
+inline int sbt(int x){return __builtin_popcount(x);}
+using namespace std;
+int freq[1111111];
+int BLOCK;
+//Mo Sorting
+bool f(pair<int,pi> a, pair<int,pi> b){
+    if(a.se.fi/BLOCK == b.se.fi/BLOCK)
+        return a.se.se>b.se.se;
+    return a.se.fi/BLOCK>b.se.fi/BLOCK;
+}
+int main() {
+    //fast_io()
+    int n;
+    scanf("%d",&n);
+    int a[n+3];
+    for(int i=0;i<n;i++)
+        scanf("%d",&a[i]);
+    int l,r,s=0,e=0;
+    int Q;
+    vector<pair<int,pi>>q;
+    scanf("%d",&Q);
+    //block size:SQRT(N)
+    BLOCK = floor(sqrt(1.0*double(n)));
+    for(int i=0;i<Q;i++){
+        scanf("%d%d",&l,&r);
+        q.pb(mp(i,mp(l-1,r-1)));
+    }
+    int v[Q+4],ans=0;
+    sort(q.begin(),q.end(),f);  //f is comparator
+	for(int i=0;i<Q;i++){
+	    l=q[i].se.fi;
+	    r=q[i].se.se;
+	    while(s<l){
+	        freq[a[s]]--;
+	        if(!freq[a[s]])
+	            ans--;
+	        s++;
+	    }
+	    while(s>l){
+	        freq[a[s-1]]++;
+	        if(freq[a[s-1]]==1)
+	            ans++;
+	        s--;
+	    }
+	    while(e<=r){
+	        freq[a[e]]++; // mantains frequency
+	        if(freq[a[e]]==1)
+	            ans++;
+	        e++;
+	    }
+	    while(e>r+1){
+	        freq[a[e-1]]--;
+	        if(freq[a[e-1]]==0)
+	            ans--;
+	        e--;
+	    }
+	    v[q[i].fi]=ans;
+	}
+	for(int i=0;i<Q;i++)
+	    printf("%d\n",v[i]);
+	return 0;
+}