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close #4204
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acbin
2023-06-09 18:52:05 +08:00
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parent ad03086f54
commit 00282efd8b
521 changed files with 5233 additions and 7309 deletions
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93
src/main/java/com/thealgorithms/searches/BinarySearch2dArray.java
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@ -1,11 +1,12 @@
package com.thealgorithms.searches;
/*
To apply this method, the provided array must be strictly sorted. In this method, two pointers, one at 0th row
& the other at the last row are taken & the searching is done on the basis of the middle element of the middle column.
If that element is equal to target, its coordinates are returned, else if it is smaller than the target, the rows above
that element are ignored (because the elements above it will also be smaller than the target), else that element is
greater than the target, then the rows below it are ignored.
To apply this method, the provided array must be strictly sorted. In this method, two pointers, one
at 0th row & the other at the last row are taken & the searching is done on the basis of the middle
element of the middle column. If that element is equal to target, its coordinates are returned, else
if it is smaller than the target, the rows above that element are ignored (because the elements
above it will also be smaller than the target), else that element is greater than the target, then
the rows below it are ignored.
*/
public class BinarySearch2dArray {
@ -19,69 +20,55 @@ public class BinarySearch2dArray {
int startRow = 0, endRow = rowCount - 1, midCol = colCount / 2;
while (startRow < endRow - 1) {
int midRow = startRow + (endRow - startRow) / 2; //getting the index of middle row
int midRow = startRow + (endRow - startRow) / 2; // getting the index of middle row
if (arr[midRow][midCol] == target) {
return new int[] { midRow, midCol };
} else if (arr[midRow][midCol] < target) startRow =
midRow; else endRow = midRow;
return new int[] {midRow, midCol};
} else if (arr[midRow][midCol] < target)
startRow = midRow;
else
endRow = midRow;
}
/*
if the above search fails to find the target element, these conditions will be used to find the target
element, which further uses the binary search algorithm in the places which were left unexplored.
if the above search fails to find the target element, these conditions will be used to
find the target element, which further uses the binary search algorithm in the places
which were left unexplored.
*/
if (arr[startRow][midCol] == target) return new int[] {
startRow,
midCol,
};
if (arr[startRow][midCol] == target)
return new int[] {
startRow,
midCol,
};
if (arr[endRow][midCol] == target) return new int[] { endRow, midCol };
if (arr[endRow][midCol] == target) return new int[] {endRow, midCol};
if (target <= arr[startRow][midCol - 1]) return binarySearch(
arr,
target,
startRow,
0,
midCol - 1
);
if (target <= arr[startRow][midCol - 1])
return binarySearch(arr, target, startRow, 0, midCol - 1);
if (
target >= arr[startRow][midCol + 1] &&
target <= arr[startRow][colCount - 1]
) return binarySearch(arr, target, startRow, midCol + 1, colCount - 1);
if (target >= arr[startRow][midCol + 1] && target <= arr[startRow][colCount - 1])
return binarySearch(arr, target, startRow, midCol + 1, colCount - 1);
if (target <= arr[endRow][midCol - 1]) return binarySearch(
arr,
target,
endRow,
0,
midCol - 1
); else return binarySearch(
arr,
target,
endRow,
midCol + 1,
colCount - 1
);
if (target <= arr[endRow][midCol - 1])
return binarySearch(arr, target, endRow, 0, midCol - 1);
else
return binarySearch(arr, target, endRow, midCol + 1, colCount - 1);
}
static int[] binarySearch(
int[][] arr,
int target,
int row,
int colStart,
int colEnd
) {
static int[] binarySearch(int[][] arr, int target, int row, int colStart, int colEnd) {
while (colStart <= colEnd) {
int midIndex = colStart + (colEnd - colStart) / 2;
if (arr[row][midIndex] == target) return new int[] {
row,
midIndex,
}; else if (arr[row][midIndex] < target) colStart =
midIndex + 1; else colEnd = midIndex - 1;
if (arr[row][midIndex] == target)
return new int[] {
row,
midIndex,
};
else if (arr[row][midIndex] < target)
colStart = midIndex + 1;
else
colEnd = midIndex - 1;
}
return new int[] { -1, -1 };
return new int[] {-1, -1};
}
}