diff --git a/array.c b/array.c
index a19e7bb..00a6d37 100755
--- a/array.c
+++ b/array.c
@@ -4797,6 +4797,7 @@ rb_ary_sample(int argc, VALUE *argv, VALUE ary)
     VALUE opts, randgen = rb_cRandom;
     long n, len, i, j, k, idx[10];
     long rnds[numberof(idx)];
+    long memo_threshold;
 
     if (OPTHASH_GIVEN_P(opts)) {
 	VALUE rnd;
@@ -4856,6 +4857,7 @@ rb_ary_sample(int argc, VALUE *argv, VALUE ary)
 	}
 	return rb_ary_new_from_args(3, RARRAY_AREF(ary, i), RARRAY_AREF(ary, j), RARRAY_AREF(ary, k));
     }
+    memo_threshold = len < 2560 ? len / 128 : len < 5120 ? len / 64 : len < 10240 ? len / 32 : len / 16;
     if (n <= numberof(idx)) {
 	long sorted[numberof(idx)];
 	sorted[0] = idx[0] = rnds[0];
@@ -4875,6 +4877,25 @@ rb_ary_sample(int argc, VALUE *argv, VALUE ary)
 	    }
 	});
     }
+    else if (n <= memo_threshold) {
+	st_table *table = st_init_numtable_with_size(n);
+	long i2, j2;
+	st_data_t value;
+	result = rb_ary_new_capa(n);
+	RARRAY_PTR_USE(ary, ptr_ary, {
+	    RARRAY_PTR_USE(result, ptr_result, {
+		for (i=0; i<n; i++){
+		    j2 = j = RAND_UPTO(len-i) + i;
+		    i2 = i;
+		    if (st_lookup(table, (st_data_t)i, &value)) i2 = value;
+		    if (st_lookup(table, (st_data_t)j, &value)) j2 = value;
+		    st_insert(table, (st_data_t)j, (st_data_t)i2);
+		    ptr_result[i] = ptr_ary[j2];
+		}
+	    });
+	});
+	st_free_table(table);
+    }
     else {
 	result = rb_ary_dup(ary);
 	RBASIC_CLEAR_CLASS(result);