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Problem solution · Go

Codeforces 1374E2 — Reading Books (hard version)

Codeforces 1374E2 — Reading Books (hard version): a Go solution using sliding window or two pointers. Learn the idea, check the complexity, and read the full code, with credit to EndlessCheng Codeforces Go.

Technique
Sliding window or two pointers
Source
EndlessCheng Codeforces Go
Length
213 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

Sliding window or two pointers

For Codeforces 1374E2 — Reading Books (hard version), the implementation maintains a moving interval and updates only the information that enters or leaves the window.

  1. Choose the invariant that makes a window valid or useful.
  2. Advance the right boundary and add the new element.
  3. Move the left boundary only as needed while maintaining the invariant and updating the answer.

Code notes

  • 213 lines of Go from the credited upstream file 1374E2.go.
  • The implementation visibly relies on sequence storage.
  • No explicit loop blocks detected.

Complexity

Confirm that neither pointer moves backwards; if so, the scan is usually linear apart from the window’s data-structure operations.

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 1374E2 — Reading Books (hard version) · GoGo
Use this to learn the idea, then write your own version.
package main import (	"bufio"	"container/heap"	. "fmt"	"io"	"sort") // https://space.bilibili.com/206214func CF1374E2(_r io.Reader, out io.Writer) {	in := bufio.NewReader(_r)	min := func(a, b int) int {		if a > b {			return b		}		return a	}	max := func(a, b int) int {		if b > a {			return b		}		return a	} 	var n, m, k, t, t0, t1, s int	g := [4][]pair74{}	Fscan(in, &n, &m, &k)	for i := 1; i <= n; i++ {		Fscan(in, &t, &t0, &t1)		x := t0<<1 | t1		g[x] = append(g[x], pair74{t, i})	}	trash, a, b, both := g[0], g[1], g[2], g[3]	if len(a) > len(b) {		a, b = b, a	}	na, nb := len(a), len(both)	if na+nb < k || nb < k*2-m {		Fprint(out, -1)		return	} 	Sort := func(a []pair74) { sort.Slice(a, func(i, j int) bool { return a[i].t < a[j].t }) }	Sort(a)	Sort(b)	limitNa := min(m/2, m-k)	if na > limitNa {		trash = append(append(trash, a[limitNa:]...), b[limitNa:]...)		a = a[:limitNa]		b = b[:limitNa]		na = limitNa	} else {		trash = append(trash, b[na:]...)		b = b[:na]	}	for i, p := range a {		s += p.t + b[i].t	} 	Sort(both)	b0 := max(max(k-na, 0), m-2*na-len(trash))	for _, p := range both[:b0] {		s += p.t	} 	Sort(trash)	h := maxMinHeap{&maxHp{}, &minHp{}}	for _, p := range trash[:m-2*na-b0] {		h.left.push(p)	}	for _, p := range trash[m-2*na-b0:] {		h.right.push(p)	} 	s0 := s	tmp := minHp(append([]pair74{}, *h.right...))	h0 := maxMinHeap{&maxHp{append(h.left.a[:0:0], h.left.a...), h.left.s}, &tmp} 	ans := s + h.left.s	for i := na - 1; i >= k; i-- {		s -= a[i].t + b[i].t		h.push(a[i])		h.push(b[i])		ans = min(ans, s+h.left.s)	} 	if len(both) > m {		both = both[:m]	}	for j, p := range both[b0:] {		s += p.t		i := min(na, k) - 1 - j		if i >= 0 {			s -= a[i].t + b[i].t			h.push(a[i])			h.push(b[i])		}		h.l2r()		ans = min(ans, s+h.left.s)	}	Fprintln(out, ans) 	output := func() {		for _, p := range a {			Fprint(out, p.i, " ")		}		for _, p := range b {			Fprint(out, p.i, " ")		}		for _, p := range both {			Fprint(out, p.i, " ")		}		for _, p := range h.left.a {			Fprint(out, p.i, " ")		}	} 	s = s0	h = h0 	if s+h.left.s == ans {		both = both[:b0]		output()		return	} 	for i := na - 1; i >= k; i-- {		s -= a[i].t + b[i].t		h.push(a[i])		h.push(b[i])		if s+h.left.s == ans {			a = a[:i]			b = b[:i]			both = both[:b0]			output()			return		}	} 	for j, p := range both[b0:] {		s += p.t		i := min(na, k) - 1 - j		if i >= 0 {			s -= a[i].t + b[i].t			h.push(a[i])			h.push(b[i])		}		h.l2r()		if s+h.left.s == ans {			if i > 0 {				a = a[:i]				b = b[:i]			} else {				a = nil				b = nil			}			both = both[:b0+j+1]			output()			return		}	}} //func main() { CF1374E2(os.Stdin, os.Stdout) } type maxMinHeap struct {	left  *maxHp	right *minHp} func (h maxMinHeap) push(v pair74) { h.left.push(h.right.pushPop(v)) }func (h maxMinHeap) l2r()          { h.right.push(heap.Pop(h.left).(pair74)) }func (h maxMinHeap) r2l()          { h.left.push(heap.Pop(h.right).(pair74)) } type pair74 struct{ t, i int }type maxHp struct {	a []pair74	s int} func (h maxHp) Len() int            { return len(h.a) }func (h maxHp) Less(i, j int) bool  { return h.a[i].t > h.a[j].t }func (h maxHp) Swap(i, j int)       { h.a[i], h.a[j] = h.a[j], h.a[i] }func (h *maxHp) Push(v interface{}) { h.s += v.(pair74).t; h.a = append(h.a, v.(pair74)) }func (h *maxHp) Pop() interface{}   { v := h.a[len(h.a)-1]; h.s -= v.t; h.a = h.a[:len(h.a)-1]; return v }func (h *maxHp) push(v pair74)      { heap.Push(h, v) }func (h *maxHp) pushPop(v pair74) pair74 {	if h.Len() > 0 && v.t < h.a[0].t {		h.s += v.t - h.a[0].t		v, h.a[0] = h.a[0], v		heap.Fix(h, 0)	}	return v} type minHp []pair74 func (h minHp) Len() int            { return len(h) }func (h minHp) Less(i, j int) bool  { return h[i].t < h[j].t }func (h minHp) Swap(i, j int)       { h[i], h[j] = h[j], h[i] }func (h *minHp) Push(v interface{}) { *h = append(*h, v.(pair74)) }func (h *minHp) Pop() interface{}   { a := *h; v := a[len(a)-1]; *h = a[:len(a)-1]; return v }func (h *minHp) push(v pair74)      { heap.Push(h, v) }func (h minHp) pushPop(v pair74) pair74 {	if h.Len() > 0 && v.t > h[0].t {		v, h[0] = h[0], v		heap.Fix(&h, 0)	}	return v}

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