Add backspace-string-compare solution

Author: pony

src/leetcode/BackspaceStringCompare.php

@@ -0,0 +1,86 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode;
+
+class BackspaceStringCompare
+{
+    public static function backspaceCompare(string $s, string $t): bool
+    {
+        if (empty($s) || empty($t)) {
+            return false;
+        }
+        $helper = static function (string &$s, int &$i) {
+            $n = 0;
+            while ($i >= 0 && ($n > 0 || $s[$i] === '#')) {
+                $n = $s[$i] === '#' ? $n + 1 : $n - 1;
+                $i--;
+            }
+            return $i >= 0 ? $s[$i] : '#';
+        };
+        [$i, $j] = [strlen($s) - 1, strlen($t) - 1];
+        while ($i >= 0 || $j >= 0) {
+            $p = $helper($s, $i);
+            $q = $helper($t, $j);
+            if ($p !== $q) {
+                return false;
+            }
+            $i--;
+            $j--;
+        }
+
+        return true;
+    }
+
+    public static function backspaceCompare2(string $s, string $t): bool
+    {
+        if (empty($s) || empty($t)) {
+            return false;
+        }
+        [$i, $j] = [strlen($s) - 1, strlen($t) - 1];
+        $m = $n = 0;
+        while (true) {
+            while ($i >= 0 && ($m > 0 || $s[$i] === '#')) {
+                $m += $s[$i] === '#' ? 1 : -1;
+                $i--;
+            }
+            while ($j >= 0 && ($n > 0 || $t[$j] === '#')) {
+                $n += $t[$j] === '#' ? 1 : -1;
+                $j--;
+            }
+            if ($i >= 0 && $j >= 0 && $s[$i] === $t[$j]) {
+                $i--;
+                $j--;
+            } else {
+                break;
+            }
+        }
+
+        return $i === -1 && $j === -1;
+    }
+
+    public static function backspaceCompare3(string $s, string $t): bool
+    {
+        if (empty($s) || empty($t)) {
+            return false;
+        }
+        $helper = static function (string $s, array $stack) {
+            $n = strlen($s);
+            for ($i = 0; $i < $n; $i++) {
+                if ($s[$i] === '#') {
+                    if (!$stack) {
+                        continue;
+                    }
+                    array_pop($stack);
+                } else {
+                    array_push($stack, $s[$i]);
+                }
+            }
+            return $stack;
+        };
+        [$p, $q] = [$helper($s, []), $helper($t, [])];
+
+        return $p === $q;
+    }
+}

tests/leetcode/BackspaceStringCompareTest.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode\tests;
+
+use PHPUnit\Framework\TestCase;
+use leetcode\BackspaceStringCompare;
+
+class BackspaceStringCompareTest extends TestCase
+{
+    public function testBackspaceCompare(): void
+    {
+        self::assertTrue(BackspaceStringCompare::backspaceCompare('ab#c', 'ad#c'));
+        self::assertTrue(BackspaceStringCompare::backspaceCompare('ab##', 'c#d#'));
+        self::assertTrue(BackspaceStringCompare::backspaceCompare('a##c', '#a#c'));
+        self::assertFalse(BackspaceStringCompare::backspaceCompare('a#c', 'b'));
+    }
+
+    public function testBackspaceCompare2(): void
+    {
+        self::assertTrue(BackspaceStringCompare::backspaceCompare2('ab#c', 'ad#c'));
+        self::assertTrue(BackspaceStringCompare::backspaceCompare2('ab##', 'c#d#'));
+        self::assertTrue(BackspaceStringCompare::backspaceCompare2('a##c', '#a#c'));
+        self::assertFalse(BackspaceStringCompare::backspaceCompare2('a#c', 'b'));
+    }
+
+    public function testBackspaceCompare3(): void
+    {
+        self::assertTrue(BackspaceStringCompare::backspaceCompare3('ab#c', 'ad#c'));
+        self::assertTrue(BackspaceStringCompare::backspaceCompare3('ab##', 'c#d#'));
+        self::assertTrue(BackspaceStringCompare::backspaceCompare3('a##c', '#a#c'));
+        self::assertFalse(BackspaceStringCompare::backspaceCompare3('a#c', 'b'));
+    }
+}