Add solution 341

leetcode/0341.Flatten-Nested-List-Iterator/341. Flatten Nested List Iterator.go

@@ -0,0 +1,72 @@
+package leetcode
+
+import "container/list"
+
+// This is the interface that allows for creating nested lists.
+// You should not implement it, or speculate about its implementation
+type NestedInteger struct {
+}
+
+// Return true if this NestedInteger holds a single integer, rather than a nested list.
+func (this NestedInteger) IsInteger() bool { return true }
+
+// Return the single integer that this NestedInteger holds, if it holds a single integer
+// The result is undefined if this NestedInteger holds a nested list
+// So before calling this method, you should have a check
+func (this NestedInteger) GetInteger() int { return 0 }
+
+// Set this NestedInteger to hold a single integer.
+func (n *NestedInteger) SetInteger(value int) {}
+
+// Set this NestedInteger to hold a nested list and adds a nested integer to it.
+func (this *NestedInteger) Add(elem NestedInteger) {}
+
+// Return the nested list that this NestedInteger holds, if it holds a nested list
+// The list length is zero if this NestedInteger holds a single integer
+// You can access NestedInteger's List element directly if you want to modify it
+func (this NestedInteger) GetList() []*NestedInteger { return nil }
+
+type NestedIterator struct {
+	stack *list.List
+}
+
+type listIndex struct {
+	nestedList []*NestedInteger
+	index      int
+}
+
+func Constructor(nestedList []*NestedInteger) *NestedIterator {
+	stack := list.New()
+	stack.PushBack(&listIndex{nestedList, 0})
+	return &NestedIterator{stack}
+}
+
+func (this *NestedIterator) Next() int {
+	if !this.HasNext() {
+		return -1
+	}
+	last := this.stack.Back().Value.(*listIndex)
+	nestedList, i := last.nestedList, last.index
+	val := nestedList[i].GetInteger()
+	last.index++
+	return val
+}
+
+func (this *NestedIterator) HasNext() bool {
+	stack := this.stack
+	for stack.Len() > 0 {
+		last := stack.Back().Value.(*listIndex)
+		nestedList, i := last.nestedList, last.index
+		if i >= len(nestedList) {
+			stack.Remove(stack.Back())
+		} else {
+			val := nestedList[i]
+			if val.IsInteger() {
+				return true
+			}
+			last.index++
+			stack.PushBack(&listIndex{val.GetList(), 0})
+		}
+	}
+	return false
+}