overflow_v2.c

#include <stdint.h>
#include <stdbool.h>

bool overflow(int64_t *A, size_t n) {
    //All elements of A are non-negative
    A[n] = INT64_MAX;
    A[n + 1] = 1;     //any positive value

    size_t i = 0;
    int64_t sum = A[0];

    while (sum >= A[i]) {
        sum += A[++i];
    }

    if (i < n) return true;
    return false;
}