Data commit

Task/Stable-marriage-problem/C/stable-marriage-problem.c

@@ -0,0 +1,134 @@
+#include <stdio.h>
+
+int verbose = 0;
+enum {
+	clown = -1,
+	abe, bob, col, dan, ed, fred, gav, hal, ian, jon,
+	abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan,
+};
+const char *name[] = {
+	"Abe", "Bob", "Col",  "Dan", "Ed",  "Fred", "Gav", "Hal",  "Ian", "Jon",
+	"Abi", "Bea", "Cath", "Dee", "Eve", "Fay",  "Gay", "Hope", "Ivy", "Jan"
+};
+int pref[jan + 1][jon + 1] = {
+	{ abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay },
+	{ cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay },
+	{ hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan },
+	{ ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi },
+	{ jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay },
+	{ bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay },
+	{ gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay },
+	{ abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee },
+	{ hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve },
+	{ abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope },
+
+	{ bob, fred, jon, gav, ian, abe, dan, ed, col, hal   },
+	{ bob, abe, col, fred, gav, dan, ian, ed, jon, hal   },
+	{ fred, bob, ed, gav, hal, col, ian, abe, dan, jon   },
+	{ fred, jon, col, abe, ian, hal, gav, dan, bob, ed   },
+	{ jon, hal, fred, dan, abe, gav, col, ed, ian, bob   },
+	{ bob, abe, ed, ian, jon, dan, fred, gav, col, hal   },
+	{ jon, gav, hal, fred, bob, abe, col, ed, dan, ian   },
+	{ gav, jon, bob, abe, ian, dan, hal, ed, col, fred   },
+	{ ian, col, hal, gav, fred, bob, abe, ed, jon, dan   },
+	{ ed, hal, gav, abe, bob, jon, col, ian, fred, dan   },
+};
+int pairs[jan + 1], proposed[jan + 1];
+
+void engage(int man, int woman)
+{
+	pairs[man] = woman;
+	pairs[woman] = man;
+	if (verbose) printf("%4s is engaged to %4s\n", name[man], name[woman]);
+}
+
+void dump(int woman, int man)
+{
+	pairs[man] = pairs[woman] = clown;
+	if (verbose) printf("%4s dumps %4s\n", name[woman], name[man]);
+}
+
+/* how high this person ranks that: lower is more preferred */
+int rank(int this, int that)
+{
+	int i;
+	for (i = abe; i <= jon && pref[this][i] != that; i++);
+	return i;
+}
+
+void propose(int man, int woman)
+{
+	int fiance = pairs[woman];
+	if (verbose) printf("%4s proposes to %4s\n", name[man], name[woman]);
+
+	if (fiance == clown) {
+		engage(man, woman);
+	} else if (rank(woman, man) < rank(woman, fiance)) {
+		dump(woman, fiance);
+		engage(man, woman);
+	}
+}
+
+int covet(int man1, int wife2)
+{
+	if (rank(man1, wife2) < rank(man1, pairs[man1]) &&
+			rank(wife2, man1) < rank(wife2, pairs[wife2])) {
+		printf( "    %4s (w/ %4s) and %4s (w/ %4s) prefer each other"
+			" over current pairing.\n",
+			name[man1], name[pairs[man1]], name[wife2], name[pairs[wife2]]
+		);
+		return 1;
+	}
+	return 0;
+}
+
+int thy_neighbors_wife(int man1, int man2)
+{	/* +: force checking all pairs; "||" would shortcircuit */
+	return covet(man1, pairs[man2]) + covet(man2, pairs[man1]);
+}
+
+int unstable()
+{
+	int i, j, bad = 0;
+	for (i = abe; i < jon; i++) {
+		for (j = i + 1; j <= jon; j++)
+			if (thy_neighbors_wife(i, j)) bad = 1;
+	}
+	return bad;
+}
+
+int main()
+{
+	int i, unengaged;
+	/* init: everyone marries the clown */
+	for (i = abe; i <= jan; i++)
+		pairs[i] = proposed[i] = clown;
+
+	/* rounds */
+	do {
+		unengaged = 0;
+		for (i = abe; i <= jon; i++) {
+		//for (i = abi; i <= jan; i++) { /* could let women propose */
+			if (pairs[i] != clown) continue;
+			unengaged = 1;
+			propose(i, pref[i][++proposed[i]]);
+		}
+	} while (unengaged);
+
+	printf("Pairing:\n");
+	for (i = abe; i <= jon; i++)
+		printf("  %4s - %s\n", name[i],
+			pairs[i] == clown ? "clown" : name[pairs[i]]);
+
+	printf(unstable()
+		? "Marriages not stable\n" /* draw sad face here */
+		: "Stable matchup\n");
+
+	printf("\nBut if Bob and Fred were to swap:\n");
+	i = pairs[bob];
+	engage(bob, pairs[fred]);
+	engage(fred, i);
+	printf(unstable() ? "Marriages not stable\n" : "Stable matchup\n");
+
+	return 0;
+}