/
minPathMatrix.go
134 lines (112 loc) · 2.44 KB
/
minPathMatrix.go
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package main
import (
"math"
)
type minPathMatrix struct {
limit int
input [][]int64
m [][]int64
}
func newMinPathMatrix(limit int, input [][]int64) minPathMatrix {
return minPathMatrix{
limit: limit,
input: input,
m: makeMatrix(limit),
}
}
func (mm minPathMatrix) buildMinPathMatrix(r, c int) {
for i := 0; i < mm.limit; i++ {
for j := 0; j < mm.limit; j++ {
mm.m[i][j] = math.MaxInt64
}
}
mm.m[r][c] = mm.input[r][c]
for i := r; i > 0; i-- {
mm.m[i-1][0] = mm.m[i][0] + mm.input[i-1][0]
}
mm.buildDownRightMatrix()
for i := 0; i < mm.limit; i++ {
for j := 0; j < mm.limit; j++ {
if mm.canGo(i, j, up) {
chechRes, newMin := mm.checkNewMin(i, j, up)
if chechRes {
mm.updateCell(i, j, up, newMin)
}
}
}
}
}
func (mm minPathMatrix) buildDownRightMatrix() {
for i := 0; i < mm.limit; i++ {
for j := 0; j < mm.limit; j++ {
fromLeft := int64(math.MaxInt64)
fromUp := int64(math.MaxInt64)
if mm.canGo(i, j, left) {
leftR, leftC := mm.goDirection(i, j, left)
fromLeft = mm.m[leftR][leftC] + mm.input[i][j]
}
if mm.canGo(i, j, up) {
upR, upC := mm.goDirection(i, j, up)
fromUp = mm.m[upR][upC] + mm.input[i][j]
}
minFrom := fromUp
if fromLeft < fromUp {
minFrom = fromLeft
}
if minFrom < mm.m[i][j] {
mm.m[i][j] = minFrom
}
}
}
}
func (mm minPathMatrix) checkNewMin(r, c int, goingTo direction) (bool, int64) {
if !mm.canGo(r, c, goingTo) {
return false, 0
}
nr, nc := mm.goDirection(r, c, goingTo)
newMin := mm.m[r][c] + mm.input[nr][nc]
return newMin < mm.m[nr][nc], newMin
}
func (mm minPathMatrix) updateCell(r, c int, goingTo direction, newMin int64) {
nr, nc := mm.goDirection(r, c, goingTo)
// update this cell
mm.m[nr][nc] = newMin
comingFrom := goingTo.opposite()
dirs := comingFrom.others()
for _, currDirection := range dirs {
if mm.canGo(nr, nc, currDirection) {
chechRes, newCurrMin := mm.checkNewMin(nr, nc, currDirection)
if chechRes {
mm.updateCell(nr, nc, currDirection, newCurrMin)
}
}
}
}
func (mm minPathMatrix) canGo(i, j int, dir direction) bool {
switch dir {
case left:
return j > 0
case down:
return i < mm.limit-1
case right:
return j < mm.limit-1
case up:
return i > 0
}
return false
}
func (mm minPathMatrix) goDirection(r, c int, dir direction) (nr, nc int) {
nr = r
nc = c
switch dir {
case left:
nc--
case down:
nr++
case right:
nc++
case up:
nr--
}
return
}