Author: Jan Christoph Ebersbach <jceb@e-jc.de>
URL: http://dwm.suckless.org/patches/zoomswap
This patch swaps the current window with the previous master when zooming.

Index: dwm/dwm.c
===================================================================
--- dwm/dwm.c.orig
+++ dwm/dwm.c
@@ -236,6 +236,7 @@ static int xerrorstart(Display *dpy, XEr
 static void zoom(const Arg *arg);
 
 /* variables */
+static Client *prevzoom = NULL;
 static const char broken[] = "broken";
 static char stext[256];
 static int screen;
@@ -2109,14 +2110,38 @@ void
 zoom(const Arg *arg)
 {
 	Client *c = selmon->sel;
+	Client *at = NULL, *cold, *cprevious = NULL;
 
 	if (!selmon->lt[selmon->sellt]->arrange
 	|| (selmon->sel && selmon->sel->isfloating))
 		return;
-	if (c == nexttiled(selmon->clients))
-		if (!c || !(c = nexttiled(c->next)))
-			return;
-	pop(c);
+	if (c == nexttiled(selmon->clients)) {
+		at = findbefore(prevzoom);
+		if (at)
+			cprevious = nexttiled(at->next);
+		if (!cprevious || cprevious != prevzoom) {
+			prevzoom = NULL;
+			if(!c || !(c = nexttiled(c->next)))
+				return;
+		} else
+			c = cprevious;
+	}
+	cold = nexttiled(selmon->clients);
+	if (c != cold && !at)
+		at = findbefore(c);
+	detach(c);
+	attach(c);
+	/* swap windows instead of pushing the previous one down */
+	if (c != cold && at) {
+		prevzoom = cold;
+		if(cold && at != cold) {
+			detach(cold);
+			cold->next = at->next;
+			at->next = cold;
+		}
+	}
+	focus(c);
+	arrange(c->mon);
 }
 
 int
Index: dwm/zoomswap.c
===================================================================
--- /dev/null
+++ dwm/zoomswap.c
@@ -0,0 +1,10 @@
+static Client * findbefore(Client *c);
+
+Client *
+findbefore(Client *c) {
+	Client *tmp;
+	if(c == selmon->clients)
+		return NULL;
+	for(tmp = selmon->clients; tmp && tmp->next != c; tmp = tmp->next) ;
+	return tmp;
+}
Index: dwm/config.def.h
===================================================================
--- dwm/config.def.h.orig
+++ dwm/config.def.h
@@ -59,6 +59,7 @@ static char dmenumon[2] = "0"; /* compon
 static const char *dmenucmd[] = { "dmenu_run", "-m", dmenumon, "-fn", dmenufont, "-nb", col_gray1, "-nf", col_gray3, "-sb", col_cyan, "-sf", col_gray4, NULL };
 static const char *termcmd[]  = { "st", NULL };
 
+#include "zoomswap.c"
 static Key keys[] = {
 	/* modifier                     key        function        argument */
 	{ MODKEY,                       XK_p,      spawn,          {.v = dmenucmd } },