49 lines
1.4 KiB
Dart
49 lines
1.4 KiB
Dart
/**
|
|
* File: binary_search_edge.dart
|
|
* Created Time: 2023-08-14
|
|
* Author: liuyuxin (gvenusleo@gmail.com)
|
|
*/
|
|
|
|
import 'binary_search_insertion.dart';
|
|
|
|
/* Binary search for the leftmost target */
|
|
int binarySearchLeftEdge(List<int> nums, int target) {
|
|
// Equivalent to finding the insertion point of target
|
|
int i = binarySearchInsertion(nums, target);
|
|
// Did not find target, thus return -1
|
|
if (i == nums.length || nums[i] != target) {
|
|
return -1;
|
|
}
|
|
// Found target, return index i
|
|
return i;
|
|
}
|
|
|
|
/* Binary search for the rightmost target */
|
|
int binarySearchRightEdge(List<int> nums, int target) {
|
|
// Convert to finding the leftmost target + 1
|
|
int i = binarySearchInsertion(nums, target + 1);
|
|
// j points to the rightmost target, i points to the first element greater than target
|
|
int j = i - 1;
|
|
// Did not find target, thus return -1
|
|
if (j == -1 || nums[j] != target) {
|
|
return -1;
|
|
}
|
|
// Found target, return index j
|
|
return j;
|
|
}
|
|
|
|
/* Driver Code */
|
|
void main() {
|
|
// Array with duplicate elements
|
|
List<int> nums = [1, 3, 6, 6, 6, 6, 6, 10, 12, 15];
|
|
print("\nArray nums = $nums");
|
|
|
|
// Binary search for left and right boundaries
|
|
for (int target in [6, 7]) {
|
|
int index = binarySearchLeftEdge(nums, target);
|
|
print("Index of the leftmost element $target = $index");
|
|
index = binarySearchRightEdge(nums, target);
|
|
print("Index of the rightmost element $target = $index");
|
|
}
|
|
}
|