feat: add php solution to lcof2 problem: No.012 (doocs#1109)

Author: Qiu-IT

lcof2/剑指 Offer II 012. 左右两边子数组的和相等/README.md

@@ -143,6 +143,31 @@ public:
 };
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer
+     */
+    function pivotIndex($nums) {
+        $sum = 0;
+        $pre = 0;
+        for ($i = 0; $i < count($nums); $i++) {
+            $sum += $nums[$i];
+        }
+        for ($i = 0; $i < count($nums); $i++) {
+            if ($pre === $sum - $pre - $nums[$i]) {
+                return $i;
+            }
+            $pre += $nums[$i];
+        }
+        return -1;
+    }
+}
+```
+
 ### **...**
 
 ```

lcof2/剑指 Offer II 012. 左右两边子数组的和相等/Solution.php

@@ -0,0 +1,20 @@
+class Solution {
+    /**
+     * @param Integer[] $nums
+     * @return Integer
+     */
+    function pivotIndex($nums) {
+        $sum = 0;
+        $pre = 0;
+        for ($i = 0; $i < count($nums); $i++) {
+            $sum += $nums[$i];
+        }
+        for ($i = 0; $i < count($nums); $i++) {
+            if ($pre === $sum - $pre - $nums[$i]) {
+                return $i;
+            }
+            $pre += $nums[$i];
+        }
+        return -1;
+    }
+}