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Problem solution · Go

Codeforces 70D — Professor's task

Codeforces 70D — Professor's task: 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
215 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 70D — Professor's task, 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

  • 215 lines of Go from the credited upstream file 70D.go.
  • The implementation keeps its working state in language-native values and containers.
  • 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 70D — Professor's task · GoGo
Use this to learn the idea, then write your own version.
package main import (	"bufio"	"cmp"	. "fmt"	"io"	"time") // https://github.com/EndlessChengtype nodeM70[K comparable, V any] struct {	son      [2]*nodeM70[K, V]	priority uint	key      K	value    V	subSize  int} func (o *nodeM70[K, V]) size() int {	if o != nil {		return o.subSize	}	return 0} func (o *nodeM70[K, V]) maintain() {	o.subSize = 1 + o.son[0].size() + o.son[1].size()} func (o *nodeM70[K, V]) rotate(d int) *nodeM70[K, V] {	x := o.son[d^1]	o.son[d^1] = x.son[d]	x.son[d] = o	o.maintain()	x.maintain()	return x} type treapM70[K comparable, V any] struct {	rd         uint	root       *nodeM70[K, V]	comparator func(a, b K) int} func (t *treapM70[K, V]) fastRand() uint {	t.rd ^= t.rd << 13	t.rd ^= t.rd >> 17	t.rd ^= t.rd << 5	return t.rd} func (t *treapM70[K, V]) size() int   { return t.root.size() }func (t *treapM70[K, V]) empty() bool { return t.size() == 0 } func (t *treapM70[K, V]) _put(o *nodeM70[K, V], key K, value V) *nodeM70[K, V] {	if o == nil {		o = &nodeM70[K, V]{priority: t.fastRand(), key: key, value: value}	} else {		c := t.comparator(key, o.key)		if c == 0 {			o.value = value		} else {			d := 0			if c > 0 {				d = 1			}			o.son[d] = t._put(o.son[d], key, value)			if o.son[d].priority > o.priority {				o = o.rotate(d ^ 1)			}		}	}	o.maintain()	return o} func (t *treapM70[K, V]) put(key K, value V) { t.root = t._put(t.root, key, value) } func (t *treapM70[K, V]) _delete(o *nodeM70[K, V], key K) *nodeM70[K, V] {	if o == nil {		return nil	}	if c := t.comparator(key, o.key); c != 0 {		d := 0		if c > 0 {			d = 1		}		o.son[d] = t._delete(o.son[d], key)	} else {		if o.son[1] == nil {			return o.son[0]		}		if o.son[0] == nil {			return o.son[1]		}		d := 0		if o.son[0].priority > o.son[1].priority {			d = 1		}		o = o.rotate(d)		o.son[d] = t._delete(o.son[d], key)	}	o.maintain()	return o} func (t *treapM70[K, V]) delete(key K) { t.root = t._delete(t.root, key) } func (t *treapM70[K, V]) lowerBoundIndex(key K) (kth int) {	for o := t.root; o != nil; {		c := t.comparator(key, o.key)		if c < 0 {			o = o.son[0]		} else if c > 0 {			kth += o.son[0].size() + 1			o = o.son[1]		} else { // 相等			kth += o.son[0].size()			break		}	}	return} func (t *treapM70[K, V]) kth(k int) (o *nodeM70[K, V]) {	if k < 0 || k >= t.root.size() {		return	}	for o = t.root; o != nil; {		leftSize := o.son[0].size()		if k < leftSize {			o = o.son[0]		} else {			k -= leftSize + 1			if k < 0 {				break			}			o = o.son[1]		}	}	return} func newMap70[K cmp.Ordered, V any]() *treapM70[K, V] {	return &treapM70[K, V]{		rd:         uint(time.Now().UnixNano())/2 + 1,		comparator: cmp.Compare[K],	}} func cf70D(in io.Reader, _w io.Writer) {	out := bufio.NewWriter(_w)	defer out.Flush()	det := func(x1, y1, x2, y2 int) int { return x1*y2 - x2*y1 }	_remove := func(t *treapM70[int, int], i int) bool {		if i <= 0 || i+1 >= t.size() {			return false		}		pre := t.kth(i - 1)		cur := t.kth(i)		nxt := t.kth(i + 1)		if det(cur.key-pre.key, cur.value-pre.value, nxt.key-pre.key, nxt.value-pre.value) >= 0 {			t.delete(cur.key)			return true		}		return false	}	contains := func(t *treapM70[int, int], x, y int) bool {		i := t.lowerBoundIndex(x)		if i == t.size() {			return false		}		cur := t.kth(i)		if cur.key == x {			return y <= cur.value		}		if i == 0 {			return false		}		pre := t.kth(i - 1)		return det(cur.key-pre.key, cur.value-pre.value, x-pre.key, y-pre.value) <= 0	}	insert := func(t *treapM70[int, int], x, y int) bool {		if contains(t, x, y) {			return false		}		t.put(x, y)		idx := t.lowerBoundIndex(x)		for j := idx + 1; _remove(t, j); {		}		for j := idx - 1; _remove(t, j); j-- {		}		return true	}	top := newMap70[int, int]()  // 上凸包	down := newMap70[int, int]() // 下凸包（y 取反） 	var q, op, x, y int	Fscan(in, &q)	for range q {		Fscan(in, &op, &x, &y)		if op == 1 {			insert(top, x, y)			insert(down, x, -y)		} else if contains(top, x, y) && contains(down, x, -y) {			Fprintln(out, "YES")		} else {			Fprintln(out, "NO")		}	}} //func main() { cf70D(bufio.NewReader(os.Stdin), os.Stdout) }

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