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@@ -0,0 +1,85 @@
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+type pair struct { // The presentation of the board is the key!
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+ _1 rune
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+ _2 int
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+}
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+
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+const INF int = 1e9
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+
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+func findMinStep(board string, hand string) int {
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+ li := list.New()
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+ n := len(board)
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+ runes := []rune(board)
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+ prev := pair{runes[0], 1}
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+ for i := 1; i < n; i++ {
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+ if runes[i] == prev._1 {
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+ prev._2++
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+ } else {
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+ li.PushBack(prev)
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+ prev = pair{runes[i], 1}
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+ }
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+ }
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+ li.PushBack(prev)
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+ m := make(map[rune]int)
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+ for _, r := range hand {
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+ m[r]++
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+ }
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+ // R, Y, B, G, W
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+ if min := dfs(li, &m); min == INF {
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+ return -1
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+ } else {
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+ return min
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+ }
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+}
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+
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+func dfs(li *list.List, m *map[rune]int) int {
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+ clearBoard(li)
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+ if li.Len() == 0 {
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+ return 0
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+ } else if len(*m) == 0 {
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+ return INF
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+ }
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+ min := INF
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+ for it := li.Front(); it != nil; it = it.Next() {
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+ p := it.Value.(pair)
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+ if cnt, ok := (*m)[p._1]; ok && 3 <= cnt+p._2 {
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+ need := 3 - p._2
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+ p._2 = 3
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+ it.Value = p
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+ (*m)[p._1] = cnt - need
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+ if cnt == need {
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+ delete(*m, p._1)
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+ }
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+ nli := list.New()
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+ nli.PushBackList(li)
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+ ret := dfs(nli, m) + need
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+ if ret < min {
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+ min = ret
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+ }
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+ p._2 -= need
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+ it.Value = p
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+ (*m)[p._1] = cnt
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+ }
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+ }
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+ return min
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+}
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+
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+func clearBoard(li *list.List) {
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+ it := li.Front()
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+ for it != nil {
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+ if nxt := it.Next(); nxt != nil && nxt.Value.(pair)._1 == it.Value.(pair)._1 {
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+ p := pair{it.Value.(pair)._1, it.Value.(pair)._2 + nxt.Value.(pair)._2}
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+ it.Value = p
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+ li.Remove(nxt)
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+ } else if 3 <= it.Value.(pair)._2 {
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+ pre := it.Prev()
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+ li.Remove(it)
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+ if pre != nil {
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+ it = pre
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+ } else {
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+ it = nxt
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+ }
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+ } else {
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+ it = nxt
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+ }
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+ }
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+}
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