Gale Shapley

Gale Shapley/GaleShapley.java

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+// Java program for stable marriage problem 
+import java.util.*; 
+
+class GaleShapley
+{ 
+
+// Number of Men or Women 
+static int N = 4; 
+
+// This function returns true if woman 
+// 'w' prefers man 'm1' over man 'm' 
+static boolean wPrefersM1OverM(int prefer[][], int w, 
+							int m, int m1) 
+{ 
+	// Check if w prefers m over 
+	// her current engagment m1 
+	for (int i = 0; i < N; i++) 
+	{ 
+		// If m1 comes before m in lisr of w, 
+		// then w prefers her current engagement, 
+		// don't do anything 
+		if (prefer[w][i] == m1) 
+			return true; 
+
+		// If m cmes before m1 in w's list, 
+		// then free her current engagement 
+		// and engage her with m 
+		if (prefer[w][i] == m) 
+		return false; 
+	} 
+	return false; 
+} 
+
+// Prints stable matching for N boys and 
+// N girls. Boys are numbered as 0 to 
+// N-1. Girls are numbereed as N to 2N-1. 
+static void stableMarriage(int prefer[][]) 
+{ 
+	// Stores partner of women. This is our 
+	// output array that stores paing information. 
+	// The value of wPartner[i] indicates the partner 
+	// assigned to woman N+i. Note that the woman 
+	// numbers between N and 2*N-1. The value -1 
+	// indicates that (N+i)'th woman is free 
+	int wPartner[] = new int[N]; 
+
+	// An array to store availability of men. 
+	// If mFree[i] is false, then man 'i' is 
+	// free, otherwise engaged. 
+	boolean mFree[] = new boolean[N]; 
+
+	// Initialize all men and women as free 
+	Arrays.fill(wPartner, -1); 
+	int freeCount = N; 
+
+	// While there are free men 
+	while (freeCount > 0) 
+	{ 
+		// Pick the first free man 
+		// (we could pick any) 
+		int m; 
+		for (m = 0; m < N; m++) 
+			if (mFree[m] == false) 
+				break; 
+
+		// One by one go to all women 
+		// according to m's preferences. 
+		// Here m is the picked free man 
+		for (int i = 0; i < N && 
+						mFree[m] == false; i++) 
+		{ 
+			int w = prefer[m][i]; 
+
+			// The woman of preference is free, 
+			// w and m become partners (Note that 
+			// the partnership maybe changed later). 
+			// So we can say they are engaged not married 
+			if (wPartner[w - N] == -1) 
+			{ 
+				wPartner[w - N] = m; 
+				mFree[m] = true; 
+				freeCount--; 
+			} 
+
+			else // If w is not free 
+			{ 
+				// Find current engagement of w 
+				int m1 = wPartner[w - N]; 
+
+				// If w prefers m over her current engagement m1, 
+				// then break the engagement between w and m1 and 
+				// engage m with w. 
+				if (wPrefersM1OverM(prefer, w, m, m1) == false) 
+				{ 
+					wPartner[w - N] = m; 
+					mFree[m] = true; 
+					mFree[m1] = false; 
+				} 
+			} // End of Else 
+		} // End of the for loop that goes 
+		// to all women in m's list 
+	} // End of main while loop 
+
+
+// Print the solution 
+System.out.println("Woman Man"); 
+for (int i = 0; i < N; i++) 
+{ 
+	System.out.print(" "); 
+	System.out.println(i + N + "	 " + 
+						wPartner[i]); 
+} 
+} 
+
+// Driver Code 
+public static void main(String[] args) 
+{ 
+	int prefer[][] = new int[][]{{7, 5, 6, 4}, 
+								{5, 4, 6, 7}, 
+								{4, 5, 6, 7}, 
+								{4, 5, 6, 7}, 
+								{0, 1, 2, 3}, 
+								{0, 1, 2, 3}, 
+								{0, 1, 2, 3}, 
+								{0, 1, 2, 3}}; 
+	stableMarriage(prefer); 
+} 
+} 
+