42
41

Delete article

Deleted articles cannot be recovered.

Draft of this article would be also deleted.

Are you sure you want to delete this article?

More than 5 years have passed since last update.

AtCoder に登録したら解くべき精選過去問 10 問を PHP で解いてみた

Last updated at Posted at 2018-03-21

はじめに

@drkenさんの記事 AtCoder に登録したら次にやること ~ これだけ解けば十分闘える!過去問精選 10 問 ~ には記事中で取り上げている過去問をいろいろな言語で解いた記事がまとめられています。ですが、PHPで解いた記事は今のところ見あたらなかったのでやってみました。

各問題の詳細は AtCoder Beginners Selection を参照してください。

第 1 問: ABC 086 A - Product (100 点)

<?php
echo array_product(explode(' ', fgets(STDIN))) % 2 ? 'Odd' : 'Even';
?>

第 2 問: ABC 081 A - Placing Marbles (100 点)

<?php
echo substr_count(fgets(STDIN), 1);
?>

第 3 問: ABC 081 B - Shift Only (200 点)

<?php
$n = fgets(STDIN);
$a = explode(' ', fgets(STDIN));
$min = 30;
for ($i = 0; $i < $n; $i++) {
    for ($j = 0; $a[$i] % 2 == 0; $j++) {
        $a[$i] /= 2;
    }
    $min = min($j, $min);
}
echo $min;
?>

第 4 問: ABC 087 B - Coins (200 点)

<?php
$a = fgets(STDIN);
$b = fgets(STDIN);
$c = fgets(STDIN);
$x = fgets(STDIN);
$result = 0;
for ($i = 0; $i <= $a; $i++) {
    for ($j = 0; $j <= $b; $j++) {
        for ($k = 0; $k <= $c; $k++) {
            if (500 * $i + 100 * $j + 50 * $k == $x) {
                $result++;
            }
        }
    }
}
echo $result;
?>

第 5 問: ABC 083 B - Some Sums (200 点)

<?php
function sum($n) {
    $s = 0;
    while ($n > 0) {
        $s += $n % 10;
        $n /= 10;
    }
    return $s;
}
 
list($n, $a, $b) = explode(' ', fgets(STDIN));
$total = 0;
for ($i = 1; $i <= $n; $i++) {
    $s = sum($i);
    if ($s >= $a && $s <= $b) {
        $total += $i;
    }
}
echo $total;
?>

第 6 問: ABC 088 B - Card Game for Two (200 点)

<?php
$n = fgets(STDIN);
$a = explode(' ', fgets(STDIN));
rsort($a);
$p = 0;
for ($i = 0; $i < $n; $i++) {
    if ($i % 2 === 0) {
        $p += $a[$i];
    } else {
        $p -= $a[$i];
    }
}
echo $p;
?>

第 7 問: ABC 085 B - Kagami Mochi (200 点)

<?php
$n = fgets(STDIN);
$num = [];
for ($i = 0; $i < $n; $i++) {
    $num[] = trim(fgets(STDIN));
}
echo count(array_unique($num));
?>

第 8 問: ABC 085 C - Otoshidama (300 点)

<?php
list($n, $y) = explode(' ', fgets(STDIN));
$r10000 = -1;
$r5000 = -1;
$r1000 = -1;
for ($a = 0; $a <= $n; $a++) {
    for ($b = 0; $a + $b <= $n; $b++) {
        $c = $n - $a - $b;
        if (10000 * $a + 5000 * $b + 1000 * $c == $y) {
            $r10000 = $a;
            $r5000 = $b;
            $r1000 = $c;
        }
    }
}
printf('%d %d %d', $r10000, $r5000, $r1000);
?>

第 9 問: ABC 049 C - Daydream (300 点)

<?php
$s = strrev(trim(fgets(STDIN)));
$divide = ['dream', 'dreamer', 'erase', 'eraser'];
foreach ($divide as $k => $v) {
    $divide[$k] = strrev($v);
}
$can = true;
for ($i = 0; $i < strlen($s);) {
    $can2 = false;
    foreach ($divide as $v) {
        if (strpos($s, $v, $i) === $i) {
            $can2 = true;
            $i += strlen($v);
        }
    }
    if (! $can2) {
        $can = false;
        break;
    }
}
echo $can ? 'YES' : 'NO';
?>

第 10 問: ABC 086 C - Traveling (300 点)

<?php
$n = fgets(STDIN);
$t = [0];
$x = [0];
$y = [0];
for ($i = 0; $i < $n; $i++) {
    list($t[$i + 1], $x[$i + 1], $y[$i + 1]) = explode(' ', fgets(STDIN));
}
$can = true;
for ($i = 0; $i < $n; $i++) {
    $dt = $t[$i + 1] - $t[$i];
    $dist = abs($x[$i + 1] - $x[$i]) + abs($y[$i + 1] - $y[$i]);
    if ($dt < $dist) {
        $can = false;
    }
    if ($dist % 2 !== $dt % 2) {
        $can = false;
    }
}
echo $can ? 'Yes' : 'No';
?>
42
41
0

Register as a new user and use Qiita more conveniently

  1. You get articles that match your needs
  2. You can efficiently read back useful information
  3. You can use dark theme
What you can do with signing up
42
41

Delete article

Deleted articles cannot be recovered.

Draft of this article would be also deleted.

Are you sure you want to delete this article?