Created
July 26, 2018 17:13
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Merge Sort
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public class Merge | |
{ | |
private Merge() { } | |
private static void merge( Comparable[] a, Comparable[] aux, int lo, int mid, int hi ) | |
{ | |
assert isSorted( a, lo, mid ); | |
assert isSorted( a, mid + 1, hi ); | |
for ( int k = lo; k <= hi; k++ ) | |
{ | |
aux[ k ] = a[ k ]; | |
} | |
int i = lo, j = mid+1; | |
for ( int k = lo; k <= hi; k++ ) | |
{ | |
if ( i > mid ) a[ k ] = aux[ j++ ]; | |
else if ( j > hi ) a[ k ] = aux[ i++ ]; | |
else if ( less( aux[ j ], aux[ i ] ) ) a[ k ] = aux[ j++ ]; | |
else a[ k ] = aux[ i++ ]; | |
} | |
assert isSorted( a, lo, hi ); | |
} | |
private static void sort( Comparable[] a, Comparable[] aux, int lo, int hi ) | |
{ | |
if ( hi <= lo ) return; | |
int mid = lo + ( hi - lo ) / 2; | |
sort( a, aux, lo, mid ); | |
sort( a, aux, mid + 1, hi ); | |
merge( a, aux, lo, mid, hi ); | |
} | |
public static void sort( Comparable[] a ) | |
{ | |
Comparable[] aux = new Comparable[ a.length ]; | |
sort( a, aux, 0, a.length - 1 ); | |
assert isSorted( a ); | |
} | |
private static boolean less( Comparable v, Comparable w ) | |
{ return v.compareTo( w ) < 0; } | |
private static boolean isSorted( Comparable[] a ) | |
{ return isSorted( a, 0, a.length - 1 ); } | |
private static boolean isSorted( Comparable[] a, int lo, int hi ) | |
{ | |
for ( int i = lo + 1; i <= hi; i++ ) | |
if ( less( a[ i ], a[ i - 1 ] ) ) return false; | |
return true; | |
} | |
private static void merge( Comparable[] a, int[] index, int[] aux, int lo, int mid, int hi ) | |
{ | |
for ( int k = lo; k <= hi; k++ ) | |
{ | |
aux[ k ] = index[ k ]; | |
} | |
int i = lo, j = mid+1; | |
for ( int k = lo; k <= hi; k++ ) | |
{ | |
if ( i > mid ) index[ k ] = aux[ j++ ]; | |
else if ( j > hi ) index[ k ] = aux[ i++ ]; | |
else if ( less( a[ aux[ j ] ], a[ aux[ i ] ] ) ) index[ k ] = aux[ j++ ]; | |
else index[ k ] = aux[ i++ ]; | |
} | |
} | |
public static int[] indexSort( Comparable[] a ) | |
{ | |
int n = a.length; | |
int[] index = new int[ n ]; | |
for ( int i = 0; i < n; i++ ) | |
index[ i ] = i; | |
int[] aux = new int[ n ]; | |
sort( a, index, aux, 0, n - 1 ); | |
return index; | |
} | |
private static void sort( Comparable[] a, int[] index, int[] aux, int lo, int hi ) | |
{ | |
if ( hi <= lo ) return; | |
int mid = lo + ( hi - lo ) / 2; | |
sort( a, index, aux, lo, mid ); | |
sort( a, index, aux, mid + 1, hi ); | |
merge( a, index, aux, lo, mid, hi ); | |
} | |
private static void show( Comparable[] a ) | |
{ | |
for ( int i = 0; i < a.length; i++ ) | |
{ | |
StdOut.println( a[ i ] ); | |
} | |
} | |
public static void main( String[] args ) | |
{ | |
String[] a = StdIn.readAllStrings(); | |
Merge.sort( a ); | |
show( a ); | |
} | |
} |
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