101 lines
2.3 KiB
Go
101 lines
2.3 KiB
Go
package diff
|
|
|
|
import "github.com/zclconf/go-cty/cty"
|
|
|
|
// longestCommonSubsequence finds a sequence of values that are common to both
|
|
// x and y, with the same relative ordering as in both collections.
|
|
//
|
|
// The approached used here is a "naive" one, assuming that both x and y will
|
|
// generally be small in the use-cases cty is aimed at. For larger lists
|
|
// the time/space usage may be sub-optimal.
|
|
//
|
|
// A pair of lists may have multiple longest common subsequences. In that
|
|
// case, the one selected by this function is undefined.
|
|
func longestCommonSubsequence(xs, ys []cty.Value) []cty.Value {
|
|
if len(xs) == 0 || len(ys) == 0 {
|
|
return make([]cty.Value, 0)
|
|
}
|
|
|
|
c := make([]int, len(xs)*len(ys))
|
|
eqs := make([]bool, len(xs)*len(ys))
|
|
w := len(xs)
|
|
|
|
for y := 0; y < len(ys); y++ {
|
|
for x := 0; x < len(xs); x++ {
|
|
eqV := xs[x].Equals(ys[y])
|
|
eq := false
|
|
if eqV.IsKnown() && eqV.True() {
|
|
eq = true
|
|
eqs[(w*y)+x] = true // equality tests can be expensive, so cache it
|
|
}
|
|
if eq {
|
|
// Sequence gets one longer than for the cell at top left,
|
|
// since we'd append a new item to the sequence here.
|
|
if x == 0 || y == 0 {
|
|
c[(w*y)+x] = 1
|
|
} else {
|
|
c[(w*y)+x] = c[(w*(y-1))+(x-1)] + 1
|
|
}
|
|
} else {
|
|
// We follow the longest of the sequence above and the sequence
|
|
// to the left of us in the matrix.
|
|
l := 0
|
|
u := 0
|
|
if x > 0 {
|
|
l = c[(w*y)+(x-1)]
|
|
}
|
|
if y > 0 {
|
|
u = c[(w*(y-1))+x]
|
|
}
|
|
if l > u {
|
|
c[(w*y)+x] = l
|
|
} else {
|
|
c[(w*y)+x] = u
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// The bottom right cell tells us how long our longest sequence will be
|
|
seq := make([]cty.Value, c[len(c)-1])
|
|
|
|
// Now we will walk back from the bottom right cell, finding again all
|
|
// of the equal pairs to construct our sequence.
|
|
x := len(xs) - 1
|
|
y := len(ys) - 1
|
|
i := len(seq) - 1
|
|
|
|
for x > -1 && y > -1 {
|
|
if eqs[(w*y)+x] {
|
|
// Add the value to our result list and then walk diagonally
|
|
// up and to the left.
|
|
seq[i] = xs[x]
|
|
x--
|
|
y--
|
|
i--
|
|
} else {
|
|
// Take the path with the greatest sequence length in the matrix.
|
|
l := 0
|
|
u := 0
|
|
if x > 0 {
|
|
l = c[(w*y)+(x-1)]
|
|
}
|
|
if y > 0 {
|
|
u = c[(w*(y-1))+x]
|
|
}
|
|
if l > u {
|
|
x--
|
|
} else {
|
|
y--
|
|
}
|
|
}
|
|
}
|
|
|
|
if i > -1 {
|
|
// should never happen if the matrix was constructed properly
|
|
panic("not enough elements in sequence")
|
|
}
|
|
|
|
return seq
|
|
}
|