HCN HSGHN L9 2021-2022 (Full Table Imple)

#include <bits/stdc++.h>
using namespace std;

constexpr int N = 1e4 + 5;

int n, m, k;
int h[N], oldh[N]; // Height of Column, oldh = h'
int L[N], R[N];    // Left Bound and Right Bound
int s[N], l;       // Imple stack
vector<int> X[N];  // X[i] is the list of X on the i-th row

void Read()
{
    cin >> n >> m >> k;

    for (int i = 1; i <= k; ++i)
    {
        int x, y;
        cin >> x >> y;

        X[x].emplace_back(y);
    }
}

void Solve()
{
    int ans(0);

    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            // Update h_j, oldh_j = h'_j
            ++h[j];
            ++oldh[j];
        }

        for (auto j : X[i])
        {
            oldh[j] = h[j]; // consider last(i,j) = 1
            h[j] = 0;       // last(i, j) = (i, j)
        }

        l = 0; // Reset Stack
        for (int j = 1; j <= m; ++j)
        {
            while (l && h[s[l]] >= oldh[j]) // Find Left Bound of Rectangle
                --l;

            L[j] = (l == 0) ? 0 : s[l];

            while (l && h[s[l]] >= h[j]) // Continue Maintain stack
                --l;

            s[++l] = j;
        }

        l = 0; // Reset Stack
        for (int j = m; j; --j)
        {
            while (l && h[s[l]] >= oldh[j]) // Find Right Bound of Rectangle
                --l;

            R[j] = (l == 0) ? m + 1 : s[l];

            while (l && h[s[l]] >= h[j]) // Continue Maintain stack
                --l;

            s[++l] = j;
        }

        for (int j = 1; j <= m; ++j)
            if(oldh[j] > h[j]) // Những cột j không tồn tại last(i,j) thì không xét
                ans = max(ans, (R[j] - L[j] - 1) * oldh[j]);
    }

    cout << ans;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    Read();
    Solve();
}

/*
Input:
4 5 4
2 3
2 5
3 1
4 4

Output:
9
*/