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#ifndef diff_hh_INCLUDED
#define diff_hh_INCLUDED
// Implementation of the linear space variant of the algorithm described in
// "An O(ND) Difference Algorithm and Its Variations"
// (http://xmailserver.org/diff2.pdf)
#include "array_view.hh"
#include "vector.hh"
#include <functional>
#include <iterator>
namespace Kakoune
{
struct Snake
{
int x, y, u, v;
enum Op { Add, Del, RevAdd, RevDel } op;
};
template<typename Iterator, typename Equal>
Snake find_end_snake_of_further_reaching_dpath(Iterator a, int N, Iterator b, int M,
const int* V, const int D, const int k, Equal eq)
{
const bool add = k == -D or (k != D and V[k-1] < V[k+1]);
// if diagonal on the right goes further along x than diagonal on the left,
// then we take a vertical edge from it to this diagonal, hence x = V[k+1]
// else, we take an horizontal edge from our left diagonal,x = V[k-1]+1
const int x = add ? V[k+1] : V[k-1]+1;
// we are by construction on diagonal k, so our position along b (y) is x - k.
const int y = x - k;
int u = x, v = y;
// follow end snake along diagonal k
while (u < N and v < M and eq(a[u], b[v]))
++u, ++v;
return { x, y, u, v, add ? Snake::Add : Snake::Del };
}
template<typename Iterator, typename Equal>
Snake find_middle_snake(Iterator a, int N, Iterator b, int M,
int* V1, int* V2, int cost_limit, Equal eq)
{
const int delta = N - M;
V1[1] = 0;
V2[1] = 0;
std::reverse_iterator<Iterator> ra{a + N}, rb{b + M};
const int max_D = std::min((M + N + 1) / 2 + 1, cost_limit);
for (int D = 0; D < max_D; ++D)
{
for (int k1 = -D; k1 <= D; k1 += 2)
{
auto p = find_end_snake_of_further_reaching_dpath(a, N, b, M, V1, D, k1, eq);
V1[k1] = p.u;
const int k2 = -(k1 - delta);
if ((delta % 2 != 0) and -(D-1) <= k2 and k2 <= (D-1) and V1[k1] + V2[k2] >= N)
return p;// return last snake on forward path, len = (2 * D - 1)
}
for (int k2 = -D; k2 <= D; k2 += 2)
{
auto p = find_end_snake_of_further_reaching_dpath(ra, N, rb, M, V2, D, k2, eq);
V2[k2] = p.u;
const int k1 = -(k2 - delta);
if ((delta % 2 == 0) and -D <= k1 and k1 <= D and V1[k1] + V2[k2] >= N)
return { N - p.u, M - p.v, N - p.x , M - p.y,
(Snake::Op)(p.op + Snake::RevAdd) };// return last snake on reverse path, len = 2 * D
}
}
// We did not find a minimal path in less than max_D iterations, iterate one more time finding the best
Snake best{};
for (int k1 = -max_D; k1 <= max_D; k1 += 2)
{
auto p = find_end_snake_of_further_reaching_dpath(a, N, b, M, V1, max_D, k1, eq);
V1[k1] = p.u;
if ((delta % 2 != 0) and p.u + p.v >= best.u + best.v and p.u <= N and p.v <= M)
best = p;
}
for (int k2 = -max_D; k2 <= max_D; k2 += 2)
{
auto p = find_end_snake_of_further_reaching_dpath(ra, N, rb, M, V2, max_D, k2, eq);
V2[k2] = p.u;
if ((delta % 2 == 0) and p.u + p.v >= best.u + best.v and p.u <= N and p.v <= M)
best = {p.x, p.y, p.u, p.v, (Snake::Op)(p.op + Snake::RevAdd)};
}
if (best.op >= Snake::RevAdd)
best = { N - best.u, M - best.v, N - best.x , M - best.y, best.op };
return best;
}
struct Diff
{
enum { Keep, Add, Remove } mode;
int len;
int posB;
};
inline void append_diff(Vector<Diff>& diffs, Diff diff)
{
if (diff.len == 0)
return;
if (not diffs.empty() and diffs.back().mode == diff.mode
and (diff.mode != Diff::Add or
diffs.back().posB + diffs.back().len == diff.posB))
diffs.back().len += diff.len;
else
diffs.push_back(diff);
}
template<typename Iterator, typename Equal>
void find_diff_rec(Iterator a, int begA, int endA,
Iterator b, int begB, int endB,
int* V1, int* V2, int cost_limit,
Equal eq, Vector<Diff>& diffs)
{
int prefix_len = 0;
while (begA != endA and begB != endB and eq(a[begA], b[begB]))
++begA, ++begB, ++prefix_len;
int suffix_len = 0;
while (begA != endA and begB != endB and eq(a[endA-1], b[endB-1]))
--endA, --endB, ++suffix_len;
append_diff(diffs, {Diff::Keep, prefix_len, 0});
const auto lenA = endA - begA, lenB = endB - begB;
if (lenA == 0)
append_diff(diffs, {Diff::Add, lenB, begB});
else if (lenB == 0)
append_diff(diffs, {Diff::Remove, lenA, 0});
else
{
auto snake = find_middle_snake(a + begA, lenA, b + begB, lenB, V1, V2, cost_limit, eq);
kak_assert(snake.u <= lenA and snake.v <= lenB);
find_diff_rec(a, begA, begA + snake.x - (int)(snake.op == Snake::Del),
b, begB, begB + snake.y - (int)(snake.op == Snake::Add),
V1, V2, cost_limit, eq, diffs);
if (snake.op == Snake::Add)
append_diff(diffs, {Diff::Add, 1, begB + snake.y - 1});
if (snake.op == Snake::Del)
append_diff(diffs, {Diff::Remove, 1, 0});
append_diff(diffs, {Diff::Keep, snake.u - snake.x, 0});
if (snake.op == Snake::RevAdd)
append_diff(diffs, {Diff::Add, 1, begB + snake.v});
if (snake.op == Snake::RevDel)
append_diff(diffs, {Diff::Remove, 1, 0});
find_diff_rec(a, begA + snake.u + (int)(snake.op == Snake::RevDel), endA,
b, begB + snake.v + (int)(snake.op == Snake::RevAdd), endB,
V1, V2, cost_limit, eq, diffs);
}
append_diff(diffs, {Diff::Keep, suffix_len, 0});
}
template<typename Iterator, typename Equal = std::equal_to<>>
Vector<Diff> find_diff(Iterator a, int N, Iterator b, int M, Equal eq = Equal{})
{
const int max = 2 * (N + M) + 1;
Vector<int> data(2*max);
Vector<Diff> diffs;
constexpr int cost_limit = 1000;
find_diff_rec(a, 0, N, b, 0, M, &data[N+M], &data[max + N+M], cost_limit, eq, diffs);
return diffs;
}
}
#endif // diff_hh_INCLUDED
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