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Problem solution · Go

Codeforces 1463E — Plan of Lectures

Codeforces 1463E — Plan of Lectures: a Go solution using direct simulation. Learn the idea, check the complexity, and read the full code, with credit to EndlessCheng Codeforces Go.

Technique
Direct simulation
Source
EndlessCheng Codeforces Go
Length
174 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Direct simulation

For Codeforces 1463E — Plan of Lectures, the implementation follows the problem’s operations directly while maintaining only the state needed for the next decision.

  1. Translate each rule into one explicit state update.
  2. Maintain the invariant after every processed item.
  3. Return the accumulated state once all relevant input has been handled.

Code notes

  • 174 lines of Go from the credited upstream file 1463E.go.
  • The implementation visibly relies on sequence storage.
  • No explicit loop blocks detected.

Complexity

Count the number and nesting of passes over the input, then include the maintained containers in the memory estimate.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from EndlessCheng Codeforces Go by Σndless (EndlessCheng) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeCodeforces 1463E — Plan of Lectures · GoGo
Use this to learn the idea, then write your own version.
package main import (	"bufio"	. "fmt"	"io") // github.com/EndlessCheng/codeforces-gofunc CF1463E(_r io.Reader, _w io.Writer) {	in := bufio.NewReader(_r)	out := bufio.NewWriter(_w)	defer out.Flush() 	var n, k, v, w int	Fscan(in, &n, &k)	fa := make([]int, n)	var find func(int) int	find = func(x int) int {		if fa[x] != x {			fa[x] = find(fa[x])		}		return fa[x]	}	merge := func(from, to int) bool {		x, y := find(from), find(to)		if x == y {			return false		}		fa[x] = y		return true	}	same := func(x, y int) bool { return find(x) == find(y) }	p := make([]int, n)	to := make([]int, n)	for i := range p {		Fscan(in, &p[i])		p[i]--		to[i] = -1		fa[i] = i	}	for ; k > 0; k-- {		Fscan(in, &v, &w)		v--		w--		if !merge(w, v) {			Fprint(out, 0)			return		}		to[v] = w	} 	// 将链缩为点	g := make([][]int, n)	deg := make([]int, n)	for w, v := range p {		if v >= 0 && !same(v, w) {			v, w = fa[v], fa[w]			g[v] = append(g[v], w)			deg[w]++		}	} 	// 跑缩点后的拓扑排序	q := []int{}	for i, d := range deg {		if d == 0 && fa[i] == i {			q = append(q, i)		}	}	orders := []int{}	for len(q) > 0 {		v := q[0]		q = q[1:]		for x := v; x >= 0; x = to[x] {			orders = append(orders, x)		}		for _, w := range g[v] {			if deg[w]--; deg[w] == 0 {				q = append(q, w)			}		}	} 	if len(orders) < n {		Fprint(out, 0)		return	}	pos := make([]int, n)	for i, o := range orders {		pos[o] = i	}	// 由于把链缩为了点，还需要额外判断链上的拓扑序是否和树上的父子顺序一致	// 这一步也可以放在建图之前，见 https://codeforces.com/contest/1463/submission/101602043	for w, v := range p {		if v >= 0 && pos[v] > pos[w] {			Fprint(out, 0)			return		}	}	for _, v := range orders {		Fprint(out, v+1, " ")	}} func CF1463ESolution2(_r io.Reader, _w io.Writer) {	in := bufio.NewReader(_r)	out := bufio.NewWriter(_w)	defer out.Flush() 	var n, k, v, w, rt int	Fscan(in, &n, &k)	p := make([]int, n)	to := make([]int, n)	top := make([]int, n)	for i := range p {		Fscan(in, &p[i])		if p[i]--; p[i] < 0 {			rt = i		}		to[i] = -1		top[i] = i	}	inChain := make([]bool, n)	for ; k > 0; k-- {		Fscan(in, &v, &w)		v--		w--		to[v] = w		inChain[w] = true	} 	g := make([][]int, n)	deg := make([]int, n)	for i, c := range inChain {		if !c {			for v := i; v >= 0; v = to[v] {				top[v] = i				if p[v] >= 0 && top[p[v]] != i {					g[p[v]] = append(g[p[v]], i)					deg[i]++				}			}		}	} 	ans := []interface{}{}	q := []int{}	// rt 入度不为零的数据：	// 3 1	// 0 3 1	// 1 2	if !inChain[rt] && deg[rt] == 0 {		q = []int{rt}	}	for len(q) > 0 {		for v, q = q[0], q[1:]; v >= 0; v = to[v] {			ans = append(ans, v+1)			for _, w := range g[v] {				if deg[w]--; deg[w] == 0 {					q = append(q, w)				}			}		}	}	if len(ans) < n {		Fprint(out, 0)	} else {		Fprint(out, ans...)	}} //func main() { CF1463E(os.Stdin, os.Stdout) }

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