105 lines
3.0 KiB
Java
105 lines
3.0 KiB
Java
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/*This is a Java Program to find number of occurences of a given number using binary search approach. The time complexity of the following program is O (log n).*/
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/*
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* Java Program to Find the Number of occurrences of a given Number using Binary Search approach
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*/
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import java.util.Scanner;
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public class NumberOfOccurences
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{
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public static void main(String[] args)
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{
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Scanner scan = new Scanner(System.in);
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System.out.println("Enter number of elements in sorted array");
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int N = scan.nextInt();
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int[] arr = new int[ N ];
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/* Accept N elements */
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System.out.println("Enter "+ N +" sorted elements");
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for (int i = 0; i < N; i++)
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arr[i] = scan.nextInt();
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System.out.println("Enter number to find occurences");
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int num = scan.nextInt();
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int f = occur(arr, num);
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if (f == -1)
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System.out.println("No occurence");
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else
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System.out.println("Occurences = "+ f);
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}
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public static int occur(int[] arr, int num)
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{
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/* find first index */
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int l1 = first(arr, num);
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/* find last index */
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int l2 = last(arr, num);
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if (l1 == -1 || l2 == -1)
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return -1;
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return l2 - l1 + 1;
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}
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public static int first(int[] arr, int num)
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{
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if (arr[0] == num)
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return 0;
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int start = 0, end = arr.length - 1;
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int mid = (start + end) / 2;
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int flag = 0;
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while (!(arr[mid] == num && arr[mid - 1] < arr[mid]))
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{
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if (start == end)
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{
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flag = 1;
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break;
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}
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if (arr[mid] >= num)
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end = mid - 1;
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if (arr[mid] < num)
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start = mid + 1;
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mid = (start + end) / 2;
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}
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if (flag == 0)
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return mid;
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return -1;
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}
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public static int last(int[] arr, int num)
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{
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if (arr[arr.length - 1] == num)
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return arr.length - 1;
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int start = 0, end = arr.length - 1;
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int mid = (start + end) / 2;
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int flag = 0;
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while (!(arr[mid] == num && arr[mid + 1] > arr[mid]))
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{
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if (start == end)
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{
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flag = 1;
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break;
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}
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if (arr[mid] > num)
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end = mid - 1;
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if (arr[mid] <= num)
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start = mid + 1;
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mid = (start + end) / 2;
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}
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if (flag == 0)
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return mid;
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return -1;
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}
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}
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/*
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Enter number of elements in sorted array
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10
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Enter 10 sorted elements
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1 1 3 3 3 3 4 4 4 5
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Enter number to find occurences
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3
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Occurences = 4
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Enter number of elements in sorted array
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10
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Enter 10 sorted elements
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1 1 3 3 3 3 4 4 4 5
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Enter number to find occurences
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5
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Occurences = 1
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