Arrays swap

cpp/Algorithms.h

@@ -147,7 +147,7 @@ void countingSort(array<int> &a, int k) {
 	array<int> b(a.length);
 	for (int i = a.length-1; i >= 0; i--)
 		b[--c[a[i]]] = a[i];
-	a = b;
+	a.swap(b);
 }
 
 void radixSort(array<int> &a) {
@@ -162,7 +162,7 @@ void radixSort(array<int> &a) {
 			c[i] += c[i-1];
 		for (int i = a.length-1; i >= 0; i--)
 			b[--c[(a[i] >> d*p)&((1<<d)-1)]] = a[i];
-		a = b;
+		a.swap(b);
 	}
 }
 

cpp/ArrayDeque.h

@@ -47,7 +47,7 @@ void ArrayDeque<T>::clear() {
 	n = 0;
 	j = 0;
 	array<T> b(1);
-	a = b;
+	a.swap(b);
 }
 
 template<class T>
@@ -65,7 +65,7 @@ void ArrayDeque<T>::resize() {
 	array<T> b(max(1, 2*n));
 	for (int k = 0; k < n; k++)
 		b[k] = a[(j+k)%a.length];
-	a = b;
+	a.swap(b);
 	j = 0;
 }
 

cpp/ArrayQueue.h

@@ -42,7 +42,7 @@ void ArrayQueue<T>::resize() {
 	array<T> b(max(1, 2*n));
 	for (int k = 0; k < n; k++)
 		b[k] = a[(j+k)%a.length];
-	a = b;
+	a.swap(b);
 	j = 0;
 }
 

cpp/ArrayStack.h

@@ -55,7 +55,7 @@ template<class T>
 void ArrayStack<T>::clear() {
 	n = 0;
 	array<T> b(1);
-	a = b;
+	a.swap(b);
 }
 
 template <class T>
@@ -72,7 +72,7 @@ void ArrayStack<T>::resize() {
 	array<T> b(max(2 * n, 1));
 	for (int i = 0; i < n; i++)
 		b[i] = a[i];
-	a = b;
+	a.swap(b);
 }
 
 template<class T>

cpp/BinaryHeap.h

@@ -52,7 +52,7 @@ template<class T>
 void BinaryHeap<T>::resize() {
 	array<T> b(max(2*n, 1));
 	std::copy(a+0, a+n, b+0);
-	a = b;
+	a.swap(b);
 }
 
 template<class T>
@@ -62,7 +62,7 @@ void BinaryHeap<T>::sort(array<T> &b) {
 		h.a.swap(--h.n, 0);
 		h.trickleDown(0);
 	}
-	b = h.a;
+	b.swap(h.a);
 	b.reverse();
 }
 
@@ -134,7 +134,7 @@ BinaryHeap<T>::BinaryHeap() : a(1) {
 
 template<class T>
 BinaryHeap<T>::BinaryHeap(array<T> &b) : a(0) {
-	a = b;
+	a.swap(b);
 	n = a.length;
 	for (int i = n/2-1; i >= 0; i--) {
 		trickleDown(i);

cpp/ChainedHashTable.h

@@ -56,7 +56,7 @@ void ChainedHashTable<T>::resize() {
 			newTable[hash(x)].add(x);
 		}
 	}
-	t = newTable;
+	t.swap(newTable);
 }
 
 template<class T>
@@ -114,7 +114,7 @@ void ChainedHashTable<T>::clear() {
 	n = 0;
 	d = 1;
 	array<List> b(2);
-	t = b;
+	t.swap(b);
 }
 
 } /* namespace ods */

cpp/DualArrayDeque.h

@@ -97,9 +97,9 @@ void DualArrayDeque<T>::balance() {
 		for (int i = 0; i < nb; i++) {
 			ab[i] = get(nf+i);
 		}
-		front.a = af;
+		front.a.swap(af);
 		front.n = nf;
-		back.a = ab;
+		back.a.swap(ab);
 		back.n = nb;
 	}
 }

cpp/FastArrayStack.h

@@ -37,7 +37,7 @@ template<class T>
 void FastArrayStack<T>::resize() {
 	array<T> b(max(1, 2*n));
 	std::copy(a+0, a+n, b+0);
-	a = b;
+	a.swap(b);
 }
 
 template<class T>

cpp/LinearHashTable.h

@@ -112,7 +112,7 @@ void LinearHashTable<T>::resize() {
 			tnew[i] = t[k];
 		}
 	}
-	t = tnew;
+	t.swap(tnew);
 }
 
 template<class T>
@@ -121,7 +121,7 @@ void LinearHashTable<T>::clear() {
 	q = 0;
 	d = 1;
 	array<T> tnew(2, null);
-	t = tnew;
+	t.swap(tnew);
 }
 
 template<class T>

cpp/SEList.h

@@ -27,7 +27,7 @@ class SEList {
 			n = 0;
 			j = 0;
 			array<int> z(b+1);
-			a = z;
+			a.swap(z);
 		}
 		virtual ~BDeque() { }
 		// C++ Question: Why is this necessary?

cpp/array.h

@@ -31,11 +31,13 @@ class array {
 	void fill(T x);
 	virtual ~array();
 
-	array<T>& operator=(array<T> &b) {
-		if (a != NULL) delete[] a;
+	void swap(array<T> &b) {
+		T *ta = a;
 		a = b.a;
-		b.a = NULL;
+		b.a = ta;
+		int tl = length;
 		length = b.length;
+		b.length = tl;
 		return *this;
 	}
 
@@ -88,7 +90,7 @@ template<class T>
 void array<T>::copyOfRange(array<T> &a0, array<T> &a, int i, int j) {
 	array<T> b(j-i);
 	std::copy(a.a, a.a+j-i, b.a);
-	a0 = b;
+	a0.swap(b);
 }
 
 template<class T>

latex/arrays.tex

@@ -65,9 +65,9 @@ \chapter{Array-Based Lists}
 \cppimport{ods/array.array(len)}
 \cpponly{The elements of an array can be indexed:}
 \cppimport{ods/array.operator[]}
-\cpponly{Finally, when one array is assigned to another, this is just
+\cpponly{Finally, when one array is swapped with another, this is just
 a pointer manipulation that takes constant time:}
-\cppimport{ods/array.operator=}
+\cppimport{ods/array.swap(b)}
 
 \section{#ArrayStack#: Fast Stack Operations Using an Array}
 \seclabel{arraystack}
@@ -132,7 +132,7 @@ \subsection{Growing and Shrinking}
 
 The #resize()# method is fairly straightforward; it allocates a new
 array #b# whose size is $2#n#$ and copies the #n# elements of #a# into
-the first #n# positions in #b#, and then sets #a# to #b#. Thus, after a call to #resize()#, $#a.length# = 2#n#$.
+the first #n# positions in #b#, and then \javaonly{sets #a# to #b#}\cpponly{swaps #a# with #b#}. Thus, after a call to #resize()#, $#a.length# = 2#n#$.
 
 \codeimport{ods/ArrayStack.resize()}