Merge pull request wangzheng0822#278 from wangchengtao/master

修复 $this 引用错误, 添加相应注释, 调整部分代码, 与原文同步

php/12_sort/mergeSort.php

@@ -1,40 +1,48 @@
 <?php
+/*
+ * 归并排序
+ */
 
-    $arr = [4, 5, 6, 1, 3, 2];
-    $length = count($arr);
+$arr = [4, 5, 6, 1, 3, 2];
+$length = count($arr);
 
-    $p = 0;
-    $r = $length - 1;
+$p = 0;
+$r = $length - 1;
 
-    $result = $this->mergeSort($arr, $p, $r);
+$result = mergeSort($arr, $p, $r);
 
-    var_dump($result);
+var_dump($result);
 
 
-//递归调用,分解数组
 function mergeSort(array $arr, $p, $r)
 {
+    return mergeSortRecursive($arr, $p, $r);
+}
+
+// 递归调用函数
+function mergeSortRecursive(array $arr, $p, $r)
+{
+    // 递归终止条件
     if ($p >= $r) {
         return [$arr[$r]];
     }
+
+    // 取 p 到 r 之间的中间位置 q
     $q = (int)(($p + $r) / 2);
 
-    $left = $this->mergeSort($arr, $p, $q);
-    $right = $this->mergeSort($arr, $q + 1, $r);
-    return $this->merge($left, $right);
+    // 分治递归
+    $left = mergeSortRecursive($arr, $p, $q);
+    $right = mergeSortRecursive($arr, $q + 1, $r);
+    return merge($left, $right);
 }
 
-//合并
+// 合并
 function merge(array $left, array $right)
 {
     $tmp = [];
-
-    $i = 0;
-
-    $j = 0;
+    $i = $j = 0;
 
     $leftLength = count($left);
-
     $rightLength = count($right);
 
     do {
@@ -43,24 +51,23 @@ function merge(array $left, array $right)
         } else {
             $tmp[] = $right[$j++];
         }
-
     } while ($i < $leftLength && $j < $rightLength);
 
-
     $start = $i;
     $end = $leftLength;
     $copyArr = $left;
 
+    // 判断哪个子数组中有剩余的数据
     if ($j < $rightLength) {
         $start = $j;
         $end = $rightLength;
         $copyArr = $right;
     }
 
-    for (; $start < $end; $start++) {
-        $tmp[] = $copyArr[$start];
-    }
+    // 将剩余的数据拷贝到临时数组 tmp
+    do {
+        $tmp[] = $copyArr[$start++];
+    } while ($start < $end);
 
     return $tmp;
-
 }