add some

Author: beyondyyh

algorithms/README.md

@@ -69,7 +69,8 @@
 |1108|[地址无效化](https://leetcode-cn.com/problems/defanging-an-ip-address/)|[go](./mystring/1108.defangIPaddr.go)|S|
 |1213|[三个有序数组的交集](https://leetcode-cn.com/problems/intersection-of-three-sorted-arrays/)|[go](./myarray/1213.arraysIntersection.go)|S|
 |1367|[二叉树中的列表](https://leetcode-cn.com/problems/linked-list-in-binary-tree/)|[go](./tree/1367.isSubPath.go)|M|
-|-|-|-|-|
+|offer100||||
+|22|[链表中倒数第k个节点](https://leetcode-cn.com/problems/lian-biao-zhong-dao-shu-di-kge-jie-dian-lcof/)|[go](./offer100/22.getKthFromEnd.go)|S|
+|40|[最小的k个数](https://leetcode-cn.com/problems/zui-xiao-de-kge-shu-lcof/)|[go](./offer100/40.getLeastNumbers.go)|S|
 |58|[左旋转字符串](https://leetcode-cn.com/problems/zuo-xuan-zhuan-zi-fu-chuan-lcof/)|[go](./offer100/58.reverseLeftWords.go)|S|
-|22|[链表中倒数第k个节点](https://leetcode-cn.com/problems/lian-biao-zhong-dao-shu-di-kge-jie-dian-lcof/)|[go](./offer100/22.getKthFromEnd.go)|S
 ||||[:top:](#Top)|

algorithms/mystring/20.isValid.go

@@ -75,3 +75,30 @@ func isValid2(s string) bool {
 
 	return stack.IsEmpty()
 }
+
+// 遍历字符串，当遇到左括号时，先把右括号入栈，
+// 当遇到右括号时，如果此时栈为空则为无效，不为空则出栈一个元素(该元素应该是右括号才算匹配)与当前遍历到的元素对比是否相等，不相等说明肯定不匹配
+// 遍历结束判断栈是否为空
+func isValid3(s string) bool {
+	// 奇数长度，肯定不匹配
+	if len(s)%2 == 1 {
+		return false
+	}
+
+	stack := kit.NewStack()
+	for _, char := range s {
+		switch char {
+		case '(':
+			stack.Push(')')
+		case '[':
+			stack.Push(']')
+		case '{':
+			stack.Push('}')
+		default: // 说明有多余的括号
+			if stack.IsEmpty() || char != (stack.Pop()).(rune) {
+				return false
+			}
+		}
+	}
+	return stack.IsEmpty()
+}

algorithms/mystring/20.isValid_test.go

@@ -25,6 +25,9 @@ func Test_isValid(t *testing.T) {
 			if output := isValid2(tt.input); output != tt.expected {
 				t.Errorf("isValid2(%s)=%t, expected=%t", tt.input, output, tt.expected)
 			}
+			if output := isValid3(tt.input); output != tt.expected {
+				t.Errorf("isValid3(%s)=%t, expected=%t", tt.input, output, tt.expected)
+			}
 		})
 	}
 }

algorithms/offer100/22.getKthFromEnd_test.go

@@ -1,9 +1,10 @@
 package offer100
 
 import (
-	"Leetcode/algorithms/kit"
 	"reflect"
 	"testing"
+
+	"Leetcode/algorithms/kit"
 )
 
 // run: go test -run Test_getKthFromEnd

algorithms/offer100/40.getLeastNumbers.go

@@ -0,0 +1,51 @@
+package offer100
+
+// 输入整数数组 arr ，找出其中最小的 k 个数。例如，输入4、5、1、6、2、7、3、8这8个数字，则最小的4个数字是1、2、3、4。
+// 示例 1：
+// 输入：arr = [3,2,1], k = 2
+// 输出：[1,2] 或者 [2,1]
+// 示例 2：
+// 输入：arr = [0,1,2,1], k = 1
+// 输出：[0]
+
+import (
+	"container/heap"
+)
+
+// int类型的堆
+type IntHeap []int
+
+// 利用golang标准库的container/heap实现堆
+func (h IntHeap) Len() int           { return len(h) }
+func (h IntHeap) Less(i, j int) bool { return h[i] > h[j] } // '<'是小顶堆
+func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+// Push和Pop 的receiver用指针，因为不仅修改slice的长度，还要修改其元素
+func (h *IntHeap) Push(x interface{}) {
+	*h = append(*h, x.(int))
+}
+
+func (h *IntHeap) Pop() interface{} {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+func getLeastNumbers(nums []int, k int) []int {
+	h := &IntHeap{}
+	heap.Init(h)
+	for _, num := range nums {
+		heap.Push(h, num)
+		if h.Len() > k {
+			heap.Pop(h)
+		}
+	}
+
+	res := make([]int, 0, k)
+	for h.Len() > 0 {
+		res = append(res, heap.Pop(h).(int))
+	}
+	return res
+}

algorithms/offer100/40.getLeastNumbers_test.go

@@ -0,0 +1,38 @@
+package offer100
+
+import (
+	"reflect"
+	"testing"
+)
+
+// run: go test -run -v Test_getLeastNumbers
+func Test_getLeastNumbers(t *testing.T) {
+	cases := []CaseEntry{
+		{
+			Name: "x1",
+			Input: []interface{}{
+				[]int{3, 2, 1}, 2,
+			},
+			Expected: []int{2, 1},
+		},
+		{
+			Name: "x2",
+			Input: []interface{}{
+				[]int{0, 1, 2, 1}, 1,
+			},
+			Expected: []int{0},
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.Name, func(t *testing.T) {
+			nums := c.Input.([]interface{})[0].([]int)
+			k := c.Input.([]interface{})[1].(int)
+
+			output := getLeastNumbers(nums, k)
+			if !reflect.DeepEqual(output, c.Expected.([]int)) {
+				t.Errorf("getLeastNumbers(%v, %d)=%v, expected=%v", nums, k, output, c.Expected)
+			}
+		})
+	}
+}