Submission #554203

#	Time	Username	Problem	Language	Result	Execution time	Memory
554203		SmolBrain	Strah (COCI18_strah)	C++17	110 / 110	179 ms	8268 KiB

strah

// Om Namah Shivaya
// GM in 96 days

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define endl '\n'
#define pb push_back
#define conts continue
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "YES" << endl
#define no cout << "NO" << endl
#define ff first
#define ss second
#define ceil2(x,y) ((x+y-1) / (y))
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#ifndef ONLINE_JUDGE
#define debug(x) cout << #x <<" = "; print(x); cout << endl
#else
#define debug(x)
#endif

#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)

bool iseven(ll n) {if ((n & 1) == 0) return true; return false;}

void print(ll t) {cout << t;}
void print(int t) {cout << t;}
void print(string t) {cout << t;}
void print(char t) {cout << t;}
void print(double t) {cout << t;}
void print(ld t) {cout << t;}

template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(pair <T, V> p) {cout << "{"; print(p.ff); cout << ","; print(p.ss); cout << "}";}
template <class T> void print(vector <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T> void print(set <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T> void print(multiset <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T, class V> void print(map <T, V> v) {cout << "[ "; for (auto i : v) {print(i); cout << " ";} cout << "]";}
template<typename T> void amin(T &a, T b) { a = min(a, b); }
template<typename T> void amax(T &a, T b) { a = max(a, b); }

void usaco(string filename) {
    freopen((filename + ".in").c_str(), "r", stdin);
    freopen((filename + ".out").c_str(), "w", stdout);
}

const int MOD = 1e9 + 7;
const int maxn = 1e5 + 5;
const int inf1 = 1e9 + 5;
const ll inf2 = ll(1e18) + 5;

void solve(int test_case)
{
    // reference codes (thanks to the people who wrote these codes):
    // https://oj.uz/submission/475660
    // https://github.com/galletas1712/CompetitiveProgramming/blob/master/Olympiad/COCI/COCI18-strah.cpp

    ll n, m; cin >> n >> m;
    char a[n][m];
    rep(i, n) rep(j, m) cin >> a[i][j];

    vector<ll> height(m);
    ll ans = 0;

    auto sum = [&](ll l, ll r) {
        return r * (r + 1) / 2 - l * (l - 1) / 2;
    };

    rep(i, n) {
        rep(j, m) {
            if (a[i][j] == '.') height[j]++;
            else height[j] = 0;
        }

        vector<ll> nseleft(m, -1), nseright(m, m);
        stack<ll> st;

        rep(j, m) {
            while (!st.empty() and height[j] <= height[st.top()]) {
                nseright[st.top()] = j;
                st.pop();
            }

            st.push(j);
        }

        while (!st.empty()) st.pop();

        rev(j, m - 1, 0) {
            while (!st.empty() and height[j] < height[st.top()]) {
                nseleft[st.top()] = j;
                st.pop();
            }

            st.push(j);
        }

        rep(j, m) {
            /*

            find the area of all rectangles passing through cell (i,j)

            area = summation((y - x + 1) * 1 + (y - x + 1) * 2 + ... (y - x + 1) * h) for l <= x <= j and j <= y <= r
                 = summation((y - x + 1) * h * (h + 1) / 2)
                 = summation(y - x + 1) * h * (h + 1) / 2

            how to calculate summation(y - x + 1) efficiently?

            range1 = j - l + 1
            range2 = r - j + 1

            summation(y - x + 1)
            = summation((y + 1) * range1) - summation(x * range2)
            = summation(y + 1) * range1 - summation(x) * range2

            summation(y + 1) and summation(x) can be calculated in O(1) because both x and y lie within a range and the sum of natural numbers in a range can be found out using the sum of natural numbers formula

            */

            ll l = nseleft[j] + 1, r = nseright[j] - 1;

            ll range1 = j - l + 1, range2 = r - j + 1;
            ll val = sum(j + 1, r + 1) * range1 - sum(l, j) * range2;
            val *= sum(1, height[j]);
            ans += val;
        }
    }

    cout << ans << endl;
}

int main()
{
    fastio;

    int t = 1;
    // cin >> t;
    rep1(i, t) {
        solve(i);
    }

    return 0;
}

Compilation message (stderr)

strah.cpp: In function 'void usaco(std::string)':
strah.cpp:64:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   64 |     freopen((filename + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
strah.cpp:65:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   65 |     freopen((filename + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 11 / 11
• Subtask 2: 11 / 11
• Subtask 3: 11 / 11
• Subtask 4: 11 / 11
• Subtask 5: 11 / 11
• Subtask 6: 11 / 11
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• Subtask 10: 11 / 11