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lap.cc
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lap.cc
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// longest arithmetic progression
#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
unsigned lap(std::vector<unsigned> const & data)
{
unsigned res = 0;
for (unsigned i = 0; i < data.size(); ++i) {
for (unsigned j = i; j < data.size(); ++j) {
unsigned delta = data[j] - data[i];
unsigned curr_res = 2;
unsigned prev = data[j];
for (unsigned k = j + 1; k < data.size(); ++k) {
if (data[k] - prev == delta) {
prev = data[k];
++curr_res;
}
}
using namespace std;
res = max(res, curr_res);
}
}
return res;
}
bool arithThree(std::vector<unsigned> const & data)
{
if (data.size() < 3) {
return false;
}
for (unsigned k = 1; k < data.size(); ++k) {
unsigned i = k - 1;
unsigned j = k + 1;
while (i >= 0 && j < data.size()) {
if (data[i] + data[j] == 2 * data[k]) {
return true;
}
if (data[i] + data[j] > 2 * data[k]) {
--i;
} else {
++j;
}
}
}
return false;
}
unsigned lapDyn(std::vector<unsigned> const & data)
{
if (data.size() < 3) {
return data.size();
}
struct Entry
{
unsigned delta;
unsigned len;
};
typedef std::vector<Entry> Row;
typedef std::vector<Row> Dyn;
const size_t N = data.size();
Dyn dyn(data.size(), Row(data.size(), {0, 0}));
for (unsigned row = 0; row < dyn.size(); ++row) {
dyn[row][N-1] = Entry{data[N-1] - data[row], 2};
}
unsigned maxLap = 2;
for (int col = N-2; col >= 0; --col) {
for (int row = col-1; row >= 0; --row) {
unsigned delta = data[col] - data[row];
dyn[row][col] = Entry{delta, 2};
for (unsigned k = row + 1; k < N; ++k) {
Entry const & en = dyn[col][k];
if (en.delta == delta) {
dyn[row][col].len = en.len + 1;
break;
}
}
if (dyn[row][col].len > maxLap) {
maxLap = dyn[row][col].len;
}
}
}
for (int row = 0; row < N; ++row) {
for (int col = 0; col < N; ++col) {
std::cout << std::setw(2) << dyn[row][col].len << "," << std::setw(2) << dyn[row][col].delta << "| ";
}
std::cout << std::endl;
}
return maxLap;
}
int main()
{
std::vector<unsigned> data;
while (true) {
unsigned n;
std::cin >> n;
if (!std::cin || !n) {
break;
}
data.push_back(n);
}
std::cout << lapDyn(data) << std::endl;
return 0;
}