增加(剑指Offer05.替换空格.md)：php版本

problems/剑指Offer05.替换空格.md

@@ -415,6 +415,40 @@ func replaceSpace(_ s: String) -> String {
 
 
 
+PHP：
+```php
+function replaceSpace($s){
+    $sLen = strlen($s);
+    $moreLen = $this->spaceLen($s) * 2;
+
+    $head = $sLen - 1;
+    $tail = $sLen + $moreLen - 1;
+
+    $s = $s . str_repeat(' ', $moreLen);
+    while ($head != $tail) {
+        if ($s[$head] == ' ') {
+            $s[$tail--] = '0';
+            $s[$tail--] = '2';
+            $s[$tail] = '%';
+        } else {
+            $s[$tail] = $s[$head];
+        }
+        $head--;
+        $tail--;
+    }
+    return $s;
+}
+// 统计空格个数
+function spaceLen($s){
+    $count = 0;
+    for ($i = 0; $i < strlen($s); $i++) {
+        if ($s[$i] == ' ') {
+            $count++;
+        }
+    }
+    return $count;
+}
+```
 
 
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