diff --git a/src/main/java/com/thealgorithms/others/LineSweep.java b/src/main/java/com/thealgorithms/others/LineSweep.java new file mode 100644 index 00000000..f9db1f74 --- /dev/null +++ b/src/main/java/com/thealgorithms/others/LineSweep.java @@ -0,0 +1,51 @@ +package com.thealgorithms.others; +import java.util.Arrays; +import java.util.Comparator; + +/* Line Sweep algorithm can be used to solve range problems by first sorting the list of ranges + * by the start value of the range in non-decreasing order and doing a "sweep" through the number + * line(x-axis) by incrementing the start point by 1 and decrementing the end point+1 by 1 on the + * number line. + * An overlapping range is defined as (StartA <= EndB) AND (EndA >= StartB) + * References + * https://en.wikipedia.org/wiki/Sweep_line_algorithm + * https://en.wikipedia.org/wiki/De_Morgan%27s_laws> + */ +public class LineSweep { + + /** Find Maximum end point + * param = ranges : Array of range[start,end] + * return Maximum Endpoint + */ + public static int FindMaximumEndPoint (int[][]ranges){ + Arrays.sort(ranges, Comparator.comparingInt(a->a[1])); + return ranges[ranges.length-1][1]; + } + + /** Find if any ranges overlap + * param = ranges : Array of range[start,end] + * return true if overlap exists false otherwise. + */ + public static boolean isOverlap(int[][] ranges) { + + int maximumEndPoint = FindMaximumEndPoint(ranges); + Arrays.sort(ranges, Comparator.comparingInt(a->a[0])); + int[] numberLine = new int[maximumEndPoint+2]; + for (int[] range : ranges) { + + int start = range[0]; + int end = range[1]; + + numberLine[start] += 1; + numberLine[end+1] -= 1; + } + + int current = 0; + int overlaps = 0; + for (int num : numberLine) { + current += num; + overlaps = Math.max(overlaps, current); + } + return overlaps >1 ; + } +} diff --git a/src/test/java/com/thealgorithms/others/LineSweepTest.java b/src/test/java/com/thealgorithms/others/LineSweepTest.java new file mode 100644 index 00000000..428556d4 --- /dev/null +++ b/src/test/java/com/thealgorithms/others/LineSweepTest.java @@ -0,0 +1,29 @@ +package com.thealgorithms.others; +import static org.junit.jupiter.api.Assertions.*; +import org.junit.jupiter.api.Test; +public class LineSweepTest { + + + @Test + void testForOverlap(){ + int[][]arr = {{0,10},{7,20},{15,24}}; + assertTrue(LineSweep.isOverlap(arr)); + } + + @Test + void testForNoOverlap(){ + int[][]arr = {{0,10},{11,20},{21,24}}; + assertFalse(LineSweep.isOverlap(arr)); + } + @Test + void testForOverlapWhenEndAEqualsStartBAndViceVersa(){ + int[][]arr = {{0,10},{10,20},{21,24}}; + assertTrue(LineSweep.isOverlap(arr)); + } + @Test + void testForMaximumEndPoint(){ + int[][]arr = {{10,20},{1,100},{14,16},{1,8}}; + assertEquals(100,LineSweep.FindMaximumEndPoint(arr)); + } + +}