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@@ -0,0 +1,71 @@
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+type minHeap [][3]int
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+
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+func (h minHeap) Len() int { return len(h) }
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+func (h minHeap) Less(i, j int) bool { return h[i][0] < h[j][0] }
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+func (h minHeap) Swap(i, j int) { h[i], h[j] = h[j], h[i] }
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+
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+func (h *minHeap) Push(x interface{}) {
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+ *h = append(*h, x.([3]int))
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+}
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+
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+func (h *minHeap) Pop() interface{} {
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+ l := h.Len()
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+ x := (*h)[l-1]
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+ *h = (*h)[:l-1]
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+ return x
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+}
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+
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+func cutOffTree(forest [][]int) (step int) {
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+ var h minHeap
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+ H, W := len(forest), len(forest[0])
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+ for y := range forest {
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+ for x, v := range forest[y] {
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+ if 1 < v {
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+ heap.Push(&h, [3]int{v, y, x})
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+ }
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+ }
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+ }
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+ beg := []int{0, 0}
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+ used := make([][]bool, H)
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+ for h.Len() != 0 {
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+ end := heap.Pop(&h).([3]int)
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+ for i := range used {
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+ used[i] = make([]bool, W)
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+ }
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+ ds := walk(forest, H, W, beg, end[1:], used)
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+ if ds == -1 {
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+ return -1
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+ }
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+ step += ds
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+ beg = end[1:]
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+ }
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+ return step
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+}
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+
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+var dy = []int{0, 1, 0, -1}
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+var dx = []int{1, 0, -1, 0}
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+
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+func walk(forest [][]int, H, W int, beg, end []int, used [][]bool) (step int) {
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+ queue := [][]int{beg}
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+ n := 1
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+ for len(queue) != 0 {
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+ pos := queue[0]
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+ queue = queue[1:]
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+ if pos[0] == end[0] && pos[1] == end[1] {
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+ return
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+ }
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+ for i := 0; i < 4; i++ {
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+ ny, nx := pos[0]+dy[i], pos[1]+dx[i]
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+ if 0 <= ny && ny < H && 0 <= nx && nx < W && !used[ny][nx] && forest[ny][nx] != 0 {
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+ queue = append(queue, []int{ny, nx})
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+ used[ny][nx] = true
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+ }
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+ }
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+ n--
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+ if n == 0 {
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+ step++
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+ n = len(queue)
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+ }
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+ }
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+ return -1
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+}
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