feat: add php solution to lc problem: No.2485 (doocs#1142)

Author: Qiu-IT

solution/2400-2499/2485.Find the Pivot Integer/README.md

@@ -201,6 +201,28 @@ function pivotInteger(n: number): number {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer
+     */
+    function pivotInteger($n) {
+        $sum = ($n * ($n + 1)) / 2;
+        $pre = 0;
+        for ($i = 1; $i <= $n; $i++) {
+            if ($pre + $i === $sum - $pre) {
+                return $i;
+            }
+            $pre += $i;
+        }
+        return -1;
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2400-2499/2485.Find the Pivot Integer/README_EN.md

@@ -164,6 +164,28 @@ function pivotInteger(n: number): number {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer
+     */
+    function pivotInteger($n) {
+        $sum = ($n * ($n + 1)) / 2;
+        $pre = 0;
+        for ($i = 1; $i <= $n; $i++) {
+            if ($pre + $i === $sum - $pre) {
+                return $i;
+            }
+            $pre += $i;
+        }
+        return -1;
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2400-2499/2485.Find the Pivot Integer/Solution.php

@@ -0,0 +1,17 @@
+class Solution {
+    /**
+     * @param Integer $n
+     * @return Integer
+     */
+    function pivotInteger($n) {
+        $sum = ($n * ($n + 1)) / 2;
+        $pre = 0;
+        for ($i = 1; $i <= $n; $i++) {
+            if ($pre + $i === $sum - $pre) {
+                return $i;
+            }
+            $pre += $i;
+        }
+        return -1;
+    }
+}