## FoVeOOS'11 Competition: challenge 1, in Java

Maximum of an array of integers, in Java

Auteurs: Claude Marché

Catégories: Array Data Structure

Outils: Krakatoa / Why3

Références: The COST FoVeOOS'11 Competition

see also the index (by topic, by tool, by reference, by year)

```/*

Challenge 1: Maximum in an array

Given: A non-empty integer array a.

Verify that the index returned by the method max() given below points to
an element maximal in the array.

*/

/*@ axiomatic integer_max {
@   logic integer max(integer x, integer y);
@   axiom max_is_ge : \forall integer x y; max(x,y) >= x && max(x,y) >= y;
@   axiom max_is_some : \forall integer x y; max(x,y) == x || max(x,y) == y;
@ }
@*/

public class ArrayMax {

/*@ requires a.length > 0;
@ ensures 0 <= \result < a.length &&
@   \forall integer i; 0 <= i < a.length ==> a[i] <= a[\result];
@*/
public static int max(int[] a) {
int x = 0;
int y = a.length-1;
/*@ loop_invariant 0 <= x <= y < a.length &&
@      \forall integer i;
@         0 <= i < x || y < i < a.length ==>
@         a[i] <= max(a[x],a[y]);
@ loop_variant y - x;
@*/
while (x != y) {
if (a[x] <= a[y]) x++;
else y--;
}
return x;
}

}

/*
Local Variables:
compile-command: "make ArrayMax.why3ml"
End:
*/

```