Range queries diff. array easy prob.

algos/range_queries/DifferenceArray/soln/Abhigyan_Tiwari/Solution1.cpp

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+//submission: https://cses.fi/paste/e4457766b0659c86f204fa/
+/* Given an array of n integers, your task is to process q queries of the following types:
+increase each value in range [a,b] by u ----1 a b u
+what is the value at position k?        ---2 k               */
+
+
+
+increase each value in range [a,b] by u
+what is the value at position k?
+
+#include <bits/stdc++.h>
+using namespace std;
+
+using ll = long long;
+#define all(x) (x).begin(), (x).end()
+
+const int MOD = 1e9 + 7;
+//we use iterative segment tree so max size=2^18 = 262,144 < 2e5
+
+/* The second half of the array sz to 2*sz-1 stores the leaves.
+The first half 1 to sz-1 stores the internal sums.                 */
+const int sz = 1<<18;
+ll tree[sz*2];
+void change(int i, int x){
+    i+=sz;
+    while(i){
+        tree[i]+=x;
+        i/=2;
+    }
+}
+
+ll get_sum(int l,int r){
+    ll res = 0;
+    l += sz;
+    r += sz;
+    while (l <= r) {
+        if (l % 2 == 1) res += tree[l++];
+        if (r % 2 == 0) res += tree[r--];
+        l /= 2;
+        r /= 2;
+    }
+    return res;
+}
+//we will be using difference array here 
+void solve() {
+    int n,q;
+    cin>>n>>q;
+    vector<ll> a(n);
+    for(int i=1;i<=n;i++){
+        int x;
+        cin>>x;
+        change(i,x);
+        change(i+1,-x);
+    }
+    while(q--){
+        int t; cin>>t;
+        if(t==1){
+            int l,r,u;
+            cin>>l>>r>>u;
+          //making changes: increment [l,r] index values by u 
+            change(l,u);
+            change(r+1,-u);
+        }
+        else{
+            int k; cin>>k;
+            cout<<get_sum(1,k)<<endl;
+        }
+    }
+}
+//T.C.: O(NlogN + Q*logN)
+//S.C.: O(sz)
+int main() {
+    // Fast I/O
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    solve();
+
+    return 0;
+}