68 lines
1.6 KiB
Go
68 lines
1.6 KiB
Go
// Package q1466 implements a solution for https://leetcode.com/problems/reorder-routes-to-make-all-paths-lead-to-the-city-zero/
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package q1466
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import "math"
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func walk(connections [][2][]int, minFlips []int32, node int) {
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mf := minFlips[node]
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// Walk no-flip-needed
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for _, n := range connections[node][1] {
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if mf < minFlips[n] {
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minFlips[n] = mf
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walk(connections, minFlips, n)
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}
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}
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// Walk flip-needed
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for _, n := range connections[node][0] {
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if mf+1 < minFlips[n] {
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minFlips[n] = mf + 1
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walk(connections, minFlips, n)
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}
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}
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}
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func collect(connections [][2][]int, minFlips []int32, node int, visited []bool) int32 {
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mf := minFlips[node]
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var sum int32
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for _, n := range connections[node][1] {
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if !visited[n] && mf == minFlips[n] {
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visited[n] = true
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sum += collect(connections, minFlips, n, visited) - mf
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}
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}
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for _, n := range connections[node][0] {
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if !visited[n] && mf+1 == minFlips[n] {
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visited[n] = true
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sum += collect(connections, minFlips, n, visited) - mf
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}
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}
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return sum + mf
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}
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func minReorder(n int, connections [][]int) int {
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conns := make([][2][]int, n)
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for i := range connections {
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from, to := connections[i][0], connections[i][1]
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conns[from][0] = append(conns[from][0], to)
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conns[to][1] = append(conns[to][1], from)
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}
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minFlips := make([]int32, n) // minimum flips to reach node n
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minFlips[0] = math.MaxInt32
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for i := 1; i < len(minFlips); i *= 2 {
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copy(minFlips[i:], minFlips[:i])
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}
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minFlips[0] = 0
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walk(conns, minFlips, 0)
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visited := make([]bool, n)
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return int(collect(conns, minFlips, 0, visited))
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}
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var _ = minReorder
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