Merge pull request #104 from iyoungm/master

php_12_sort_mergeSort

Author: wangzheng0822

php/12_sort/mergeSort.php

@@ -0,0 +1,66 @@
+<?php
+
+    $arr = [4, 5, 6, 1, 3, 2];
+    $length = count($arr);
+
+    $p = 0;
+    $r = $length - 1;
+
+    $result = $this->mergeSort($arr, $p, $r);
+
+    var_dump($result);
+
+
+//递归调用,分解数组
+function mergeSort(array $arr, $p, $r)
+{
+    if ($p >= $r) {
+        return [$arr[$r]];
+    }
+    $q = (int)(($p + $r) / 2);
+
+    $left = $this->mergeSort($arr, $p, $q);
+    $right = $this->mergeSort($arr, $q + 1, $r);
+    return $this->merge($left, $right);
+}
+
+//合并
+function merge(array $left, array $right)
+{
+    $tmp = [];
+
+    $i = 0;
+
+    $j = 0;
+
+    $leftLength = count($left);
+
+    $rightLength = count($right);
+
+    do {
+        if ($left[$i] <= $right[$j]) {
+            $tmp[] = $left[$i++];
+        } else {
+            $tmp[] = $right[$j++];
+        }
+
+    } while ($i < $leftLength && $j < $rightLength);
+
+
+    $start = $i;
+    $end = $leftLength;
+    $copyArr = $left;
+
+    if ($j < $rightLength) {
+        $start = $j;
+        $end = $rightLength;
+        $copyArr = $right;
+    }
+
+    for (; $start < $end; $start++) {
+        $tmp[] = $copyArr[$start];
+    }
+
+    return $tmp;
+
+}