106 lines
2.1 KiB
Go
106 lines
2.1 KiB
Go
package pacificatlanticwaterflow
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type Position struct{ X, Y int }
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func (p Position) Neighbors() []Position {
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return []Position{
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{p.X + 1, p.Y},
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{p.X - 1, p.Y},
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{p.X, p.Y + 1},
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{p.X, p.Y - 1},
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}
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}
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func (p Position) ToList() []int {
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return []int{p.Y, p.X}
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}
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type Board [][]int
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func (b Board) Get(p Position) int {
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if b.OutOfBounds(p) {
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return -1
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}
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return b[p.Y][p.X]
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}
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func (b Board) Height() int { return len(b) }
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func (b Board) Width() int { return len(b[0]) }
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func (b Board) OutOfBounds(p Position) bool {
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return p.Y < 0 || p.Y >= b.Height() || p.X < 0 || p.X >= b.Width()
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}
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type Flow struct{ Pacific, Atlantic bool }
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func (f *Flow) Merge(o Flow) {
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f.Atlantic = f.Atlantic || o.Atlantic
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f.Pacific = f.Pacific || o.Pacific
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}
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func (f Flow) Both() bool {
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return f.Pacific && f.Atlantic
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}
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func (b Board) GetFlow(p Position) Flow {
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return Flow{
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Atlantic: p.Y >= b.Height() || p.X >= b.Width(),
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Pacific: p.Y < 0 || p.X < 0,
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}
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}
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func pacificAtlanticHelper(board Board, position Position, flows map[Position]Flow) Flow {
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if flow, ok := flows[position]; ok {
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return flow
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}
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if board.OutOfBounds(position) {
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return board.GetFlow(position)
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}
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flow := Flow{}
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var top Position
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plateau := map[Position]bool{}
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unvisited := []Position{position}
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for len(unvisited) > 0 {
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top, unvisited = unvisited[len(unvisited)-1], unvisited[:len(unvisited)-1]
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if board.Get(top) < board.Get(position) {
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flow.Merge(pacificAtlanticHelper(board, top, flows))
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} else if board.Get(top) == board.Get(position) {
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if _, ok := plateau[top]; !ok {
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plateau[top] = true
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unvisited = append(unvisited, top.Neighbors()...)
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}
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}
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}
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for mem := range plateau {
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flows[mem] = flow
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}
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return flow
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}
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func PacificAtlantic(heights [][]int) [][]int {
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flows := map[Position]Flow{}
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board := Board(heights)
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for y := range board.Height() {
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for x := range board.Width() {
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pacificAtlanticHelper(board, Position{x, y}, flows)
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}
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}
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result := [][]int{}
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for position, flow := range flows {
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if flow.Both() {
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result = append(result, position.ToList())
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}
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}
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return result
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}
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