fix some bug and add cap method to array

sparse_array/array2/array2.go

@@ -5,6 +5,8 @@ type Array2 struct {
 	ysize int
 	xsize int
 	data  [][]interface{}
+
+	cap int
 }
 
 func New() *Array2 {
@@ -15,6 +17,8 @@ func NewWithCap(ysize, xsize int) *Array2 {
 	arr := &Array2{ysize: ysize, xsize: xsize}
 	arr.sizes = make([]int, arr.ysize, arr.ysize)
 	arr.data = make([][]interface{}, arr.ysize, arr.ysize)
+
+	arr.cap = arr.ysize * arr.xsize
 	return arr
 }
 
@@ -58,6 +62,10 @@ func (arr *Array2) Values() []interface{} {
 	return result
 }
 
+func (arr *Array2) Cap() int {
+	return arr.cap
+}
+
 func (arr *Array2) Grow(size int) {
 	arr.ysize += size
 	temp := make([][]interface{}, arr.ysize, arr.ysize)
@@ -67,6 +75,8 @@ func (arr *Array2) Grow(size int) {
 	tempsizes := make([]int, arr.ysize, arr.ysize)
 	copy(tempsizes, arr.sizes)
 	arr.sizes = tempsizes
+
+	arr.cap = arr.ysize * arr.xsize
 }
 
 func (arr *Array2) Set(idx int, value interface{}) {