Algorithms: Array Techniques Tutorials and Code Examples - Page 10

In Place Array Reversal in C

Reversal exchanges symmetric positions until the two pointers meet.

c

int reverse_array(int *a, size_t a_length) {
    int alg_error = 0;
    int alg_result = INT_MIN;
    errno = 0;
    if (a_length > 1000000 || (a_length && !a)) { errno = EINVAL; alg_result = INT_MIN; goto alg_cleanup; }
    int n = (int)a_length;
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    if (!(((n >= 0) && (n <= 1000000)))) { errno = EINVAL; alg_result = INT_MIN; goto alg_cleanup; }
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    if (!(((int)a_length == n))) { errno = EINVAL; alg_result = INT_MIN; goto alg_cleanup; }
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    int left = 0;

Nov 15, 2026 C

Algorithms: Array Techniques

In Place Array Reversal in Python

Reversal exchanges symmetric positions until the two pointers meet.

python

def reverse_array(a: list[int]) -> int:
    alg_require(isinstance(a, list) and len(a) <= 1000000)
    n: int = len(a)
    alg_require(n >= 0 and n <= 1000000)
    alg_require(len(a) == n)
    left: int = 0
    right: int = n - 1
    temp: int = 0
    while left < right:
        temp = a[left]
        a[left] = a[right]
        a[right] = temp

Nov 15, 2026 python

Algorithms: Array Techniques

In Place Array Reversal in JavaScript

Reversal exchanges symmetric positions until the two pointers meet.

javascript

function reverse_array(a) {
    alg_require(a instanceof Int32Array);
    let n = a.length;
    alg_require(((n >= 0) && (n <= 1000000)));
    alg_require((a.length == n));
    let left = 0;
    let right = alg_sub(n, 1);
    let temp = 0;
    while ((left < right)) {
        temp = a[left];
        a[left] = a[right];
        a[right] = temp;

Nov 15, 2026 javascript

Algorithms: Array Techniques

In Place Array Reversal in Java

Reversal exchanges symmetric positions until the two pointers meet.

java

    static int reverse_array(int[] a) {
        java.util.Objects.requireNonNull(a, "a");
        int n = a.length;
        alg_require(((n >= 0) && (n <= 1000000)));
        alg_require((a.length == n));
        int left = 0;
        int right = Math.subtractExact(n, 1);
        int temp = 0;
        while ((left < right)) {
            temp = a[left];
            a[left] = a[right];
            a[right] = temp;

Nov 15, 2026 Java

Algorithms: Array Techniques

Prefix Sum Range Query in Python

Prefix sums turn a range sum into a subtraction.

python

def range_sum(a: list[int], left: int, right: int) -> int:
    alg_require(isinstance(a, (list, tuple)) and len(a) <= 1000000)
    alg_require(type(left) is int and -2147483648 <= left <= 2147483647)
    alg_require(type(right) is int and -2147483648 <= right <= 2147483647)
    n: int = len(a)
    alg_require(n >= 0 and n <= 1000000)
    alg_require(len(a) == n)
    alg_require(left >= 0 and left <= right and (right < n))
    prefix: list[int] = [0] * alg_size(n + 1)
    i: int = 0
    while i < n:
        prefix[i + 1] = prefix[i] + a[i]

Nov 15, 2026 python