Add 归并排序

归并排序

@@ -0,0 +1,20 @@
+// 归并排序
+void merge_sort(int q[], int l, int r)
+{
+    if (l >= r) return;
+    
+    int mid = l + r >> 1;
+    merge_sort(q, l, mid);
+    merge_sort(q, mid + 1, r);
+    
+    int k = 0, i = l, j = mid + 1;
+    while (i <= mid && j <= r)
+        if (q[i] < q[j]) tmp[k ++ ] = q[i ++ ];
+        else tmp[k ++ ] = q[j ++ ];
+    
+    while (i <= mid) tmp[k ++ ] = q[i ++ ];
+    while (j <= r) tmp[k ++ ] = q[j ++ ];
+    
+    for (i = l, j = 0; i <= r; i ++, j ++ ) q[i] = tmp[j];
+}
+//复杂度说明： 在各种情况下归并排序时间复杂度均为 o(nlogn).