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Add algorithm to search for an element in 2D array (#3306)
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package com.thealgorithms.searches;
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// The search is for any array which is sorted row and column-wise too. For ex :
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// int[][] arr = { {10, 20, 30, 40},
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// {15, 25, 35, 45},
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// {18, 28, 38, 48},
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// {21, 31, 41, 51}
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// };
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// This array is sorted in both row and column manner.
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// In this two pointers are taken, the first points to the 0th row and the second one points to end column, and then the
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// element corresponding to the pointers placed in the array is compared with the target that either its equal, greater or
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// smaller than the target. If the element is equal to the target, the co-ordinates of that element is returned i.e. an
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// array of the two pointers will be returned, else if the target is greater than corresponding element then the pointer
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// pointing to the 0th row will be incremented by 1, else if the target is lesser than the corresponding element then the
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// pointer pointing to the end column will be decremented by 1. And if the element doesn't exist in the array, an array
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// {-1, -1} will be returned.
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public class RowColumnWiseSorted2dArrayBinarySearch {
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public static int[] search(int[][] matrix, int target) {
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int rowPointer = 0; //The pointer at 0th row
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int colPointer = matrix.length-1; //The pointer at end column
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while (rowPointer < matrix.length && colPointer >= 0){
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if (matrix[rowPointer][colPointer] == target)
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return new int[] {rowPointer, colPointer};
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else if (matrix[rowPointer][colPointer] < target)
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rowPointer++; //Incrementing the row pointer if the target is greater
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else
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colPointer--; //Decrementing the column pointer if the target is lesser
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}
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return new int[] {-1, -1}; //The not found condition
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}
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}
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package com.thealgorithms.searches;
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import org.junit.jupiter.api.Test;
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import java.util.*;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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public class RowColumnWiseSorted2dArrayBinarySearchTest {
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@Test
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// valid test case
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public void rowColumnSorted2dArrayBinarySearchTestMiddle() {
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int[][] arr = { {10, 20, 30, 40},
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{15, 25, 35, 45},
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{18, 28, 38, 48},
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{21, 31, 41, 51}
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};
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int target = 35;
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int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
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int[] expected = {1,2};
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System.out.println(Arrays.toString(ans));
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assertEquals(1, ans[0]);
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assertEquals(2, ans[1]);
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}
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@Test
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// valid test case
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public void rowColumnSorted2dArrayBinarySearchTestSide() {
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int[][] arr = { {10, 20, 30, 40},
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{15, 25, 35, 45},
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{18, 28, 38, 48},
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{21, 31, 41, 51}
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};
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int target = 48;
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int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
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int[] expected = {2,3};
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System.out.println(Arrays.toString(ans));
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assertEquals(2, ans[0]);
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assertEquals(3, ans[1]);
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}
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@Test
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// valid test case
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public void rowColumnSorted2dArray_BinarySearchTestUpper() {
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int[][] arr = { {10, 20, 30, 40},
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{15, 25, 35, 45},
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{18, 28, 38, 48},
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{21, 31, 41, 51}
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};
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int target = 20;
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int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
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int[] expected = {0,1};
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System.out.println(Arrays.toString(ans));
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assertEquals(0, ans[0]);
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assertEquals(1, ans[1]);
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}
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@Test
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// valid test case
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public void rowColumnSorted2dArray_BinarySearchTestUpperSide() {
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int[][] arr = { {10, 20, 30, 40},
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{15, 25, 35, 45},
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{18, 28, 38, 48},
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{21, 31, 41, 51}
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};
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int target = 40;
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int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
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int[] expected = {0,3};
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System.out.println(Arrays.toString(ans));
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assertEquals(0, ans[0]);
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assertEquals(3, ans[1]);
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}
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@Test
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// valid test case
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public void rowColumnSorted2dArray_BinarySearchTestLower() {
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int[][] arr = { {10, 20, 30, 40},
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{15, 25, 35, 45},
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{18, 28, 38, 48},
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{21, 31, 41, 51}
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};
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int target = 31;
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int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
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int[] expected = {3,1};
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System.out.println(Arrays.toString(ans));
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assertEquals(3, ans[0]);
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assertEquals(1, ans[1]);
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}
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@Test
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// valid test case
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public void rowColumnSorted2dArray_BinarySearchTestLowerSide() {
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int[][] arr = { {10, 20, 30, 40},
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{15, 25, 35, 45},
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{18, 28, 38, 48},
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{21, 31, 41, 51}
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};
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int target = 51;
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int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
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int[] expected = {3,3};
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System.out.println(Arrays.toString(ans));
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assertEquals(3, ans[0]);
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assertEquals(3, ans[1]);
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}
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@Test
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// valid test case
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public void rowColumnSorted2dArray_BinarySearchTestNotFound() {
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int[][] arr = { {10, 20, 30, 40},
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{15, 25, 35, 45},
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{18, 28, 38, 48},
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{21, 31, 41, 51}
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};
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int target = 101;
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int[] ans = RowColumnWiseSorted2dArrayBinarySearch.search(arr, target);
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int[] expected = {-1,-1};
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System.out.println(Arrays.toString(ans));
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assertEquals(-1, ans[0]);
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assertEquals(-1, ans[1]);
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}
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}
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