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Add algorithm to search for an element in 2D array (#3306)

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Shashwat Gupta
2022-10-09 14:53:36 +05:30
committed by GitHub
parent 302db81bb8
commit cce1dbd124
2 changed files with 161 additions and 0 deletions
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37
src/main/java/com/thealgorithms/searches/RowColumnWiseSorted2dArrayBinarySearch.java Normal file
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package com.thealgorithms.searches;
// The search is for any array which is sorted row and column-wise too. For ex :
// int[][] arr = { {10, 20, 30, 40},
// {15, 25, 35, 45},
// {18, 28, 38, 48},
// {21, 31, 41, 51}
// };
// This array is sorted in both row and column manner.
// In this two pointers are taken, the first points to the 0th row and the second one points to end column, and then the
// element corresponding to the pointers placed in the array is compared with the target that either its equal, greater or
// smaller than the target. If the element is equal to the target, the co-ordinates of that element is returned i.e. an
// array of the two pointers will be returned, else if the target is greater than corresponding element then the pointer
// pointing to the 0th row will be incremented by 1, else if the target is lesser than the corresponding element then the
// pointer pointing to the end column will be decremented by 1. And if the element doesn't exist in the array, an array
// {-1, -1} will be returned.
public class RowColumnWiseSorted2dArrayBinarySearch {
public static int[] search(int[][] matrix, int target) {
int rowPointer = 0; //The pointer at 0th row
int colPointer = matrix.length-1; //The pointer at end column
while (rowPointer < matrix.length && colPointer >= 0){
if (matrix[rowPointer][colPointer] == target)
return new int[] {rowPointer, colPointer};
else if (matrix[rowPointer][colPointer] < target)
rowPointer++; //Incrementing the row pointer if the target is greater
else
colPointer--; //Decrementing the column pointer if the target is lesser
}
return new int[] {-1, -1}; //The not found condition
}
}

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src/test/java/com/thealgorithms/searches/RowColumnWiseSorted2dArrayBinarySearchTest.java Normal file
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package com.thealgorithms.searches;
import org.junit.jupiter.api.Test;
import java.util.*;
import static org.junit.jupiter.api.Assertions.assertEquals;
public class RowColumnWiseSorted2dArrayBinarySearchTest {
@Test
// valid test case
public void rowColumnSorted2dArrayBinarySearchTestMiddle() {
int[][] arr = { {10, 20, 30, 40},
{15, 25, 35, 45},
{18, 28, 38, 48},
{21, 31, 41, 51}
};
int target = 35;
int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
int[] expected = {1,2};
System.out.println(Arrays.toString(ans));
assertEquals(1, ans[0]);
assertEquals(2, ans[1]);
}
@Test
// valid test case
public void rowColumnSorted2dArrayBinarySearchTestSide() {
int[][] arr = { {10, 20, 30, 40},
{15, 25, 35, 45},
{18, 28, 38, 48},
{21, 31, 41, 51}
};
int target = 48;
int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
int[] expected = {2,3};
System.out.println(Arrays.toString(ans));
assertEquals(2, ans[0]);
assertEquals(3, ans[1]);
}
@Test
// valid test case
public void rowColumnSorted2dArray_BinarySearchTestUpper() {
int[][] arr = { {10, 20, 30, 40},
{15, 25, 35, 45},
{18, 28, 38, 48},
{21, 31, 41, 51}
};
int target = 20;
int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
int[] expected = {0,1};
System.out.println(Arrays.toString(ans));
assertEquals(0, ans[0]);
assertEquals(1, ans[1]);
}
@Test
// valid test case
public void rowColumnSorted2dArray_BinarySearchTestUpperSide() {
int[][] arr = { {10, 20, 30, 40},
{15, 25, 35, 45},
{18, 28, 38, 48},
{21, 31, 41, 51}
};
int target = 40;
int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
int[] expected = {0,3};
System.out.println(Arrays.toString(ans));
assertEquals(0, ans[0]);
assertEquals(3, ans[1]);
}
@Test
// valid test case
public void rowColumnSorted2dArray_BinarySearchTestLower() {
int[][] arr = { {10, 20, 30, 40},
{15, 25, 35, 45},
{18, 28, 38, 48},
{21, 31, 41, 51}
};
int target = 31;
int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
int[] expected = {3,1};
System.out.println(Arrays.toString(ans));
assertEquals(3, ans[0]);
assertEquals(1, ans[1]);
}
@Test
// valid test case
public void rowColumnSorted2dArray_BinarySearchTestLowerSide() {
int[][] arr = { {10, 20, 30, 40},
{15, 25, 35, 45},
{18, 28, 38, 48},
{21, 31, 41, 51}
};
int target = 51;
int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
int[] expected = {3,3};
System.out.println(Arrays.toString(ans));
assertEquals(3, ans[0]);
assertEquals(3, ans[1]);
}
@Test
// valid test case
public void rowColumnSorted2dArray_BinarySearchTestNotFound() {
int[][] arr = { {10, 20, 30, 40},
{15, 25, 35, 45},
{18, 28, 38, 48},
{21, 31, 41, 51}
};
int target = 101;
int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
int[] expected = {-1,-1};
System.out.println(Arrays.toString(ans));
assertEquals(-1, ans[0]);
assertEquals(-1, ans[1]);
}
}