Data commit

Task/Mian-Chowla-sequence/Java/mian-chowla-sequence.java

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+import java.util.Arrays;
+
+public class MianChowlaSequence {
+
+    public static void main(String[] args) {
+        long start = System.currentTimeMillis();
+        System.out.println("First 30 terms of the Mian–Chowla sequence.");
+        mianChowla(1, 30);
+        System.out.println("Terms 91 through 100 of the Mian–Chowla sequence.");
+        mianChowla(91, 100);
+        long end = System.currentTimeMillis();
+        System.out.printf("Elapsed = %d ms%n", (end-start));
+    }
+
+    private static void mianChowla(int minIndex, int maxIndex) {
+        int [] sums = new int[1];
+        int [] chowla = new int[maxIndex+1];
+        sums[0] = 2;
+        chowla[0] = 0;
+        chowla[1] = 1;
+        if ( minIndex == 1 ) {
+            System.out.printf("%d ", 1);
+        }
+        int chowlaLength = 1;
+        for ( int n = 2 ; n <= maxIndex ; n++ ) {
+
+            //  Sequence is strictly increasing.
+            int test = chowla[n - 1];
+            //  Bookkeeping.  Generate only new sums.
+            int[] sumsNew = Arrays.copyOf(sums, sums.length + n);
+            int sumNewLength = sums.length;
+            int savedsSumNewLength = sumNewLength;
+
+            //  Generate test candidates for the next value of the sequence.
+            boolean found = false;
+            while ( ! found ) {
+                test++;
+                found = true;
+                sumNewLength = savedsSumNewLength;
+                //  Generate test sums
+                for ( int j = 0 ; j <= chowlaLength ; j++ ) {
+                    int testSum = (j == 0 ? test : chowla[j]) + test;
+                    boolean duplicate = false;
+
+                    //  Check if test Sum in array
+                    for ( int k = 0 ; k < sumNewLength ; k++ ) {
+                        if ( sumsNew[k] == testSum ) {
+                            duplicate = true;
+                            break;
+                        }
+                    }
+                    if ( ! duplicate ) {
+                        //  Add to array
+                        sumsNew[sumNewLength] = testSum;
+                        sumNewLength++;
+                    }
+                    else {
+                        //  Duplicate found.  Therefore, test candidate of the next value of the sequence is not OK.
+                        found = false;
+                        break;
+                    }
+                }
+            }
+
+            //  Bingo!  Now update bookkeeping.
+            chowla[n] = test;
+            chowlaLength++;
+            sums = sumsNew;
+            if ( n >= minIndex ) {
+                System.out.printf("%d %s", chowla[n], (n==maxIndex ? "\n" : ""));
+            }
+        }
+    }
+
+}