Container With Most Water in Java

// Container With Most Water in Java
//
// PURPOSE
// Two pointers maximize the area between a pair of height bars.
//
// METHOD
// Evaluate width times the smaller height. Move the smaller-height endpoint inward:
// retaining it with a shorter width cannot improve the area.
//
// COMPLEXITY
// O(n) time, O(1) auxiliary space.
//
// CONTRACT
// Nonnegative heights. Areas must fit signed 32-bit. Fewer than two bars returns 0.
// Public APIs infer array lengths except in C, which accepts pointer/length pairs. Vertex
// counts and matrix dimensions remain explicit. Arrays must contain signed 32-bit integers.
// Sorted order, correct tree topology, and caller-owned data-structure invariants are
// preconditions; checking them on every query would change query complexity.
// Scalar and shape checks are included. Value-range checks are included where needed to
// prevent invalid indexing or nontermination. Allocation sizes are capped at 4,000,000
// workspace entries. Arithmetic outside Python raises an error on 32-bit overflow; Python
// uses arbitrary precision. Native allocation failures propagate. In-place outputs may be
// partly updated after arithmetic failure. These are single-threaded, in-memory
// implementations.
//
// LANGUAGE DETAILS
// Java 17+: primitive int arrays, Arrays.binarySearch for LIS, and Math exact arithmetic.
// Invalid input throws IllegalArgumentException; arithmetic overflow throws
// ArithmeticException.
//
// EXAMPLE
// Expected return: 49.
// Run: javac AlgorithmExample.java && java AlgorithmExample
// Tests for this exact source artifact run before publication. The accompanying source
// archive includes unit cases, runtime results, and source hashes.

class AlgorithmExample {
    static void alg_require(boolean valid) { if (!valid) throw new IllegalArgumentException("invalid algorithm input"); }
    static int alg_size(int n) { alg_require(n>=0 && n<=4000000); return n; }

    static int max_container(int[] a) {
        java.util.Objects.requireNonNull(a, "a");
        int n = a.length;
        alg_require(((n >= 0) && (n <= 1000000)));
        alg_require((a.length == n));
        for (int alg_i = 0; alg_i < a.length; alg_i++) {
            int alg_value = a[alg_i];
            alg_require((alg_value >= 0));
        }
        int left = 0;
        int right = Math.subtractExact(n, 1);
        int best = 0;
        while ((left < right)) {
            best = Math.max(best, Math.multiplyExact(Math.subtractExact(right, left), Math.min(a[left], a[right])));
            if ((a[left] <= a[right])) {
                left = Math.addExact(left, 1);
            } else {
                right = Math.subtractExact(right, 1);
            }
        }
        return best;
    }

    public static void main(String[] args) {
        int[] a = new int[] {1, 8, 6, 2, 5, 4, 8, 3, 7};
        int result = max_container(a);
        System.out.println(result);
    }
}