Code Collection: VIJOS 1255

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Code Collection: VIJOS 1255

METHOD: O(n^3), Prefix Sum + O(n) Kadane's Algorithm (10/10)

#include <algorithm>
#include <iostream>
#include <cstring>
using namespace std;

int aray[305][305], psum[305][305], comp[305];
const int SMALL = -22950001;

int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int R, C;
cin >> R >> C;
for(int i=1; i<=R; i++)
for(int j=1; j<=C; j++)
{
cin >> aray[i][j];
if(aray[i][j] == 0) aray[i][j] = SMALL;
psum[i][j] = aray[i][j] + psum[i-1][j];
}
int best = aray[1][1];
for(int s=1; s<=R; s++)
for(int e=s; e<=R; e++)
{
memset(comp, 0, sizeof comp);
for(int i=1; i<=C; i++)
{
comp[i] = psum[e][i] - psum[s-1][i];
if(comp[i] < 0) comp[i] = SMALL;
}
int cmax = comp[1], cbest = comp[1];
for(int i=2; i<=C; i++)
{
cmax = max(comp[i], cmax+comp[i]);
cbest = max(cbest, cmax);
}
best = max(best, cbest);
}
cout << best << endl;
}

METHOD: O(n^4), 2-D Prefix Sum + Enumeration (6/8)

#include <algorithm>
#include <iostream>
#include <cstring>
using namespace std;

int psum[305][305], comp[305];
const int SMALL = -22950001;

int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int R, C;
cin >> R >> C;
for(int i=1; i<=R; i++)
for(int j=1; j<=C; j++)
{
int x; cin >> x;
if(x == 0) x = SMALL;
psum[i][j] = x + psum[i-1][j] + psum[i][j-1] - psum[i-1][j-1];
}
int best = psum[1][1];
for(int x1=1; x1<=R; x1++)
for(int y1=1; y1<=C; y1++)
for(int x2=x1; x2<=R; x2++)
for(int y2=y1; y2<=C; y2++)
{
best = max(best, psum[x2][y2] - psum[x1-1][y2] - psum[x2][y1-1] + psum[x1-1][y1-1]);
}
cout << best << endl;
}

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