Add solution

Author: PHOX-9

Problems/Data-structures/Day-09/sol/Ibrahim/Soln1.cpp

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+//https://codeforces.com/contest/61/submission/356643204
+#include <bits/stdc++.h>
+using namespace std;
+
+#define int long long
+#define ll long long
+#define ull unsigned long long
+#define ld long double
+#define pii pair<int,int>
+#define vi vector<int>
+#define vvi vector<vector<int>>
+#define vpi vector<pair<int,int>>
+#define all(x) (x).begin(), (x).end()
+
+
+const long long MAXN = 2e6;
+const long long MOD = 1e9 + 7;
+const int INF = 1e18;
+const ld EPS = 1e-9;
+
+
+#define fastio ios::sync_with_stdio(false); cin.tie(nullptr);
+
+#ifndef ONLINE_JUDGE
+    #define debug(x) cerr << #x << " = " << x << "\n";
+#else
+    #define debug(x)
+#endif
+
+// Utility functions
+int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
+int lcm(int a, int b) { return a / gcd(a, b) * b; }
+int mod_add(int a, int b, int m=MOD) { return ((a % m) + (b % m) + m) % m; }
+int mod_sub(int a, int b, int m=MOD) { return ((a % m) - (b % m) + m) % m; }
+int mod_mul(int a, int b, int m=MOD) { return ((a % m) * (b % m)) % m; }
+
+//Binary Exponentiation
+int binexp(int a, int b, int m=MOD) {
+    int res = 1;
+    a %= m;
+    while(b > 0) {
+        if(b & 1) res = (res * a) % m;
+        a = (a * a) % m;
+        b >>= 1;
+    }
+    return res;
+}
+
+int mod_inv(int a, int m=MOD) {
+    return binexp(a, m - 2, m);
+}
+
+long long fac[MAXN + 1];
+long long inv[MAXN + 1];
+
+long long exp(long long x, long long n, long long m) {
+  x %= m;
+  long long res = 1;
+  while (n > 0) {
+    if (n % 2 == 1) { res = res * x % m; }
+    x = x * x % m;
+    n /= 2;
+  }
+  return res;
+}
+
+void factorial() {
+  fac[0] = 1;
+  for (long long i = 1; i <= MAXN; i++) { fac[i] = fac[i - 1] * i % MOD; }
+}
+
+void inverses() {
+  inv[MAXN] = exp(fac[MAXN], MOD - 2, MOD);
+  for (long long i = MAXN; i >= 1; i--) { inv[i - 1] = inv[i] * i % MOD; }
+}
+
+long long choose(long long n, long long r) {
+  if (r > n)return 0ll;
+  return (fac[n] * inv[r] % MOD * inv[n - r] % MOD) % MOD;
+}
+
+long long catalan(long long n) {
+  return (exp(n + 1, MOD - 2, MOD) % MOD * choose(2 * n, n) % MOD) % MOD;
+}
+
+//Returns all prime numbers <=N
+vector<int> sieve(int n) {
+    vector<bool> prime(n + 1, true);
+    for (int p=2;p*p<=n;p++) {
+        if (prime[p] == true) {
+            
+            for (int i=p*p;i<=n;i+=p)
+                prime[i] = false;
+        }
+    }
+    
+    vector<int> res;
+    for (int p = 2; p <= n; p++){
+        if (prime[p]){ 
+            res.push_back(p);
+        }
+    }
+    return res;
+}
+
+//Prime factors of all numbers upto N
+vector<vector<int>> primefactors(int N)
+{
+    vvi pfac(N + 1);
+        for (int i=2;i<=N;i++){
+        if (!pfac[i].empty())
+            continue;
+
+        for (int j = i; j <= N; j += i)
+            pfac[j].push_back(i);
+    }
+            
+    return pfac;
+}
+
+//smallest prime factor of a number
+int spf(int n) {
+    if (n % 2 == 0) return 2;
+    for (int i = 3; i * i <= n; i += 2) {
+        if (n % i == 0) return i;
+    }
+    return n;
+}
+
+int power2(int p)
+{
+    int v=1ll<<p;
+    return v;
+}
+
+//Sort functions
+
+void sort(vector<int>&a)
+{
+    sort(a.begin(),a.end());
+}
+
+void psort(vector<pair<int,int>>&a)
+{
+    sort(a.begin(),a.end());
+}
+
+void rsort(vector<int>&a)
+{
+    sort(a.rbegin(),a.rend());
+}
+
+void rpsort(vector<pair<int,int>>&a)
+{
+    sort(a.rbegin(),a.rend());
+}
+
+//2-D Vector Declaration: 
+//vvi mat(n,vi(m));     // nxm matrix, all initialized to 0
+
+
+/***************Code***************/
+struct SegTree {
+public:
+ 
+    SegTree (int _n) : n (_n) {
+        tree.resize(4*n, 0);
+    }
+    
+    int query (int x, int y) {
+        return query (x, y, 0, n-1, 0);
+    }
+    
+    void update (int ind, int val) {
+        update (ind, val, 0, n-1, 0);
+    }
+ 
+private:
+    
+    vector<int> tree;
+    int n;
+    
+    int query (int x, int y, int l, int r, int i) {
+        if (r < x || l > y) return 0;
+        if (l >= x && r <= y) return tree[i];
+        
+        int m = (l+r) >> 1;
+        return (
+            query (x, y, l, m, i*2+1) +
+            query (x, y, m+1, r, i*2+2)
+        );
+    }
+    
+    void update (int ind, int val, int l, int r, int i) {
+        if (l == r) {
+            tree[i] += val;
+            return;
+        }
+        
+        int m = (l+r) >> 1;
+        if (m >= ind) update (ind, val, l, m, i*2+1);
+        else update (ind, val, m+1, r, i*2+2);
+        
+        tree[i] = tree[i*2+1] + tree[i*2+2];
+    }
+};
+
+void solve() {
+    int n,i;
+    cin>>n;
+    vi a(n);
+    vpi b(n);
+    for(i=0;i<n;i++)
+{ 
+    cin>>a[i];
+    b[i].first=a[i];
+    b[i].second=i;
+}
+    psort(b);
+
+    map <int,int> pos;
+    for(i=0;i<n;i++)
+    pos[b[i].first]=i;
+
+	SegTree tree(n);
+	int result = 0;
+
+    for(i=0;i<n;i++)
+    {
+        int ps=pos[a[i]];
+
+        int gl=tree.query(ps+1,n-1);
+        int sl=i-gl;
+        int sr=ps-sl;
+        result+=gl*sr;
+        tree.update(ps,1);
+    }
+    cout<<result<<endl;
+}
+
+
+signed main() {
+    fastio;
+    int t = 1;
+    //cin >> t;
+    while (t--) {
+        solve();
+    }
+    return 0;
+}