feat: add php solution to lc problem: No.0121 (doocs#922)

No.0121.Best Time to Buy and Sell Stock

Author: Qiu-IT

solution/0100-0199/0121.Best Time to Buy and Sell Stock/README.md

@@ -189,6 +189,27 @@ impl Solution {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param Integer[] $prices
+     * @return Integer
+     */
+    function maxProfit($prices) {
+        $win = 0;
+        $minPrice = $prices[0];
+        $len = count($prices);
+        for ($i = 1; $i < $len; $i++) {
+            $minPrice = min($minPrice, $prices[$i]);
+            $win = max($win, $prices[$i] - $minPrice);
+        }
+        return $win;
+    }
+}
+```
+
 ### **...**
 
 ```

solution/0100-0199/0121.Best Time to Buy and Sell Stock/README_EN.md

@@ -173,6 +173,27 @@ impl Solution {
 }
 ```
 
+### **PHP**
+
+```php
+class Solution {
+    /**
+     * @param Integer[] $prices
+     * @return Integer
+     */
+    function maxProfit($prices) {
+        $win = 0;
+        $minPrice = $prices[0];
+        $len = count($prices);
+        for ($i = 1; $i < $len; $i++) {
+            $minPrice = min($minPrice, $prices[$i]);
+            $win = max($win, $prices[$i] - $minPrice);
+        }
+        return $win;
+    }
+}
+```
+
 ### **...**
 
 ```

solution/0100-0199/0121.Best Time to Buy and Sell Stock/Solution.php

@@ -0,0 +1,16 @@
+class Solution {
+    /**
+     * @param Integer[] $prices
+     * @return Integer
+     */
+    function maxProfit($prices) {
+        $win = 0;
+        $minPrice = $prices[0];
+        $len = count($prices);
+        for ($i = 1; $i < $len; $i++) {
+            $minPrice = min($minPrice, $prices[$i]);
+            $win = max($win, $prices[$i] - $minPrice);
+        }
+        return $win;
+    }
+}