Binary Search
def binary_search(arr, target):
left = 0;
right = len(arr) - 1
while left <= right:
mid = left + (right - left) // 2;
if arr[mid] == target:
return mid
elif arr[mid] < target:
left = mid + 1
else:
right = mid - 1
return -1
def bisect_left(arr, target):
"""Returns the leftmost position that `target` should
go to such that the sequence remains sorted."""
left = 0
right = len(arr)
while left < right:
mid = (left + right) // 2
if arr[mid] < target:
left = mid + 1
else:
right = mid
return left
def bisect_right(arr, target):
"""Returns the rightmost position that `target` should
go to such that the sequence remains sorted."""
left = 0
right = len(arr)
while left < right:
mid = (left + right) // 2
if arr[mid] > target:
right = mid
else:
left = mid + 1
return left
print(binary_search([1, 2, 3, 10], 1) == 0)
print(binary_search([1, 2, 3, 10], 2) == 1)
print(binary_search([1, 2, 3, 10], 3) == 2)
print(binary_search([1, 2, 3, 10], 10) == 3)
print(binary_search([1, 2, 3, 10], 9) == -1)
print(binary_search([1, 2, 3, 10], 4) == -1)
print(binary_search([1, 2, 3, 10], 0) == -1)
print(binary_search([1, 2, 3, 10], 11) == -1)
print(binary_search([5, 7, 8, 10], 3) == -1)
print(bisect_left([1, 2, 3, 3, 10], 1) == 0)
print(bisect_left([1, 2, 3, 3, 10], 2) == 1)
print(bisect_left([1, 2, 3, 3, 10], 3) == 2) # First "3" is at index 2
print(bisect_left([1, 2, 3, 3, 10], 10) == 4)
# These return a valid index despite target not being in array.
print(bisect_left([1, 2, 3, 3, 10], 9) == 4)
print(bisect_left([1, 2, 3, 3, 10], 0) == 0) # Insert "0" at front
print(bisect_left([1, 2, 3, 3, 10], 11) == 5) # Insert "5" at back
print(bisect_right([1, 2, 3, 3, 10], 1) == 1)
print(bisect_right([1, 2, 3, 3, 10], 2) == 2)
print(bisect_right([1, 2, 3, 3, 10], 3) == 4) # Last "3" is at index 3, so insert new "3" at index 4
print(bisect_right([1, 2, 3, 3, 10], 10) == 5)
# These return a valid index despite target not being in array.
print(bisect_right([1, 2, 3, 3, 10], 9) == 4)
print(bisect_right([1, 2, 3, 3, 10], 0) == 0) # Insert "0" at front
print(bisect_right([1, 2, 3, 3, 10], 11) == 5) # Insert "5" at back
function binarySearch(arr, target) {
let left = 0;
let right = arr.length - 1;
while (left <= right) {
const mid = left + Math.floor((right - left) / 2);
if (arr[mid] === target) {
return mid;
}
if (arr[mid] < target) {
left = mid + 1;
} else {
right = mid - 1;
}
}
return -1;
}
console.log(binarySearch([1, 2, 3, 10], 1) === 0);
console.log(binarySearch([1, 2, 3, 10], 2) === 1);
console.log(binarySearch([1, 2, 3, 10], 3) === 2);
console.log(binarySearch([1, 2, 3, 10], 10) === 3);
console.log(binarySearch([1, 2, 3, 10], 9) === -1);
console.log(binarySearch([1, 2, 3, 10], 4) === -1);
console.log(binarySearch([1, 2, 3, 10], 0) === -1);
console.log(binarySearch([1, 2, 3, 10], 11) === -1);
console.log(binarySearch([5, 7, 8, 10], 3) === -1);
def binary_search(arr, target):
left = 0;
right = len(arr) - 1
while left <= right:
mid = left + (right - left) // 2;
if arr[mid] == target:
return mid
elif arr[mid] < target:
left = mid + 1
else:
right = mid - 1
return -1
def bisect_left(arr, target):
"""Returns the leftmost position that `target` should
go to such that the sequence remains sorted."""
left = 0
right = len(arr)
while left < right:
mid = (left + right) // 2
if arr[mid] < target:
left = mid + 1
else:
right = mid
return left
def bisect_right(arr, target):
"""Returns the rightmost position that `target` should
go to such that the sequence remains sorted."""
left = 0
right = len(arr)
while left < right:
mid = (left + right) // 2
if arr[mid] > target:
right = mid
else:
left = mid + 1
return left
print(binary_search([1, 2, 3, 10], 1) == 0)
print(binary_search([1, 2, 3, 10], 2) == 1)
print(binary_search([1, 2, 3, 10], 3) == 2)
print(binary_search([1, 2, 3, 10], 10) == 3)
print(binary_search([1, 2, 3, 10], 9) == -1)
print(binary_search([1, 2, 3, 10], 4) == -1)
print(binary_search([1, 2, 3, 10], 0) == -1)
print(binary_search([1, 2, 3, 10], 11) == -1)
print(binary_search([5, 7, 8, 10], 3) == -1)
print(bisect_left([1, 2, 3, 3, 10], 1) == 0)
print(bisect_left([1, 2, 3, 3, 10], 2) == 1)
print(bisect_left([1, 2, 3, 3, 10], 3) == 2) # First "3" is at index 2
print(bisect_left([1, 2, 3, 3, 10], 10) == 4)
# These return a valid index despite target not being in array.
print(bisect_left([1, 2, 3, 3, 10], 9) == 4)
print(bisect_left([1, 2, 3, 3, 10], 0) == 0) # Insert "0" at front
print(bisect_left([1, 2, 3, 3, 10], 11) == 5) # Insert "5" at back
print(bisect_right([1, 2, 3, 3, 10], 1) == 1)
print(bisect_right([1, 2, 3, 3, 10], 2) == 2)
print(bisect_right([1, 2, 3, 3, 10], 3) == 4) # Last "3" is at index 3, so insert new "3" at index 4
print(bisect_right([1, 2, 3, 3, 10], 10) == 5)
# These return a valid index despite target not being in array.
print(bisect_right([1, 2, 3, 3, 10], 9) == 4)
print(bisect_right([1, 2, 3, 3, 10], 0) == 0) # Insert "0" at front
print(bisect_right([1, 2, 3, 3, 10], 11) == 5) # Insert "5" at back
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