From 83348ee188af6641fd44380c9518e970fecc2485 Mon Sep 17 00:00:00 2001
From: Abhik Das <abhikdas98765@gmail.com>
Date: Thu, 22 Jul 2021 13:31:08 +0530
Subject: [PATCH] added more square root decomposition problems

---
 mo's_algo_for_subarray_sum.cpp | 68 ++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 mo's_algo_for_subarray_sum.cpp

diff --git a/mo's_algo_for_subarray_sum.cpp b/mo's_algo_for_subarray_sum.cpp
new file mode 100644
index 0000000..5e9f1be
--- /dev/null
+++ b/mo's_algo_for_subarray_sum.cpp
@@ -0,0 +1,68 @@
+#include<bits/stdc++.h>
+using namespace std;
+#define int long long
+const int N = 1e5+2, MOD = 1e9+7;
+int rootN;
+
+struct Q {
+    int idx, l, r;
+};
+
+Q q[N];
+
+bool compare(Q q1, Q q2) {
+    if(q1.l/rootN == q2.l/rootN)
+        return q1.r > q2.r;
+    
+    return q1.l/rootN < q2.l/rootN;
+}
+
+signed main() {
+    int n;
+    cin>>n;
+
+    vector<int> a(n);
+    for(int i=0; i<n; i++)
+        cin>>a[i];
+
+    rootN = sqrtl(n);
+    int queries;
+    cin>>queries;
+    for(int i=0; i<queries; i++) {
+        int l, r;
+        cin>>l>>r;
+        q[i].l = l;
+        q[i].r = r;
+        q[i].idx = i;
+    }
+
+    sort(q, q+queries, compare);
+    vector<int> ans(queries);
+    int curr_l = 0, curr_r = -1, l, r;
+    int curr_ans = 0;
+
+    for(int i=0; i<queries; i++) {
+        l = q[i].l;
+        r = q[i].r;
+        l--; r--;
+
+        while(curr_r < r)
+            curr_ans += a[++curr_r];
+
+        while(curr_l > l)
+            curr_ans += a[--curr_l];
+
+        while(curr_l < l)
+            curr_ans -= a[curr_l++];
+
+        while(curr_r > r)
+            curr_ans -= a[curr_r--];
+
+        ans[q[i].idx] = curr_ans;
+    }
+
+    for(int i=0; i<queries; i++)
+        cout<<ans[i]<<endl;
+
+    return 0;
+}
\ No newline at end of file