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Problem solution · Go

Codeforces 522B — Photo to Remember

Codeforces 522B — Photo to Remember: a Go solution using segment tree or range structure. Learn the idea, check the complexity, and read the full code, with credit to EndlessCheng Codeforces Go.

Technique
Segment tree or range structure
Source
EndlessCheng Codeforces Go
Length
89 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

Segment tree or range structure

For Codeforces 522B — Photo to Remember, the implementation stores interval information in a range-query data structure so updates and queries avoid rescanning the full input.

  1. Choose the aggregate stored for each interval or prefix.
  2. Build or initialize the structure from the input.
  3. Apply updates and combine the affected nodes to answer each query.

Code notes

  • 89 lines of Go from the credited upstream file 522B.go.
  • The implementation visibly relies on sequence storage.
  • No explicit loop blocks detected.

Complexity

Count the build once, then multiply the logarithmic update or query path by the number of 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 522B — Photo to Remember · GoGo
Use this to learn the idea, then write your own version.
package main import (	"bufio"	. "fmt"	"io") func max522B(a, b int) int {	if a > b {		return a	}	return b} type stNode522B struct {	l, r int	val  int}type segmentTree522B []stNode522B func (t segmentTree522B) _pushUp(o int) {	lo, ro := t[o<<1], t[o<<1|1]	t[o].val = max522B(lo.val, ro.val)} func (t segmentTree522B) _build(arr []int, o, l, r int) {	t[o].l, t[o].r = l, r	if l == r {		t[o].val = arr[l-1]		return	}	mid := (l + r) >> 1	t._build(arr, o<<1, l, mid)	t._build(arr, o<<1|1, mid+1, r)	t._pushUp(o)} func (t segmentTree522B) _query(o, l, r int) (res int) {	if l <= t[o].l && t[o].r <= r {		return t[o].val	}	mid := (t[o].l + t[o].r) >> 1	res = -1e9	if l <= mid {		res = max522B(res, t._query(o<<1, l, r))	}	if mid < r {		res = max522B(res, t._query(o<<1|1, l, r))	}	return} func (t segmentTree522B) init(arr []int) { t._build(arr, 1, 1, len(arr)) }func (t segmentTree522B) query(l, r int) int {	if l > r {		return 0	}	return t._query(1, l, r)} // github.com/EndlessCheng/codeforces-gofunc Sol522B(reader io.Reader, writer io.Writer) {	in := bufio.NewReader(reader)	out := bufio.NewWriter(writer)	defer out.Flush() 	var n int	Fscan(in, &n)	sumW := 0	w := make([]int, n)	h := make([]int, n)	for i := range w {		Fscan(in, &w[i], &h[i])		sumW += w[i]	} 	t := make(segmentTree522B, 4*n)	t.init(h)	for i, wi := range w {		maxH := max522B(t.query(1, i), t.query(i+2, n))		Fprint(out, (sumW-wi)*maxH, " ")	}} //func main() {//	Sol522B(os.Stdin, os.Stdout)//}

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