add: sword offer

medium/131_partition.go

@@ -0,0 +1,52 @@
+package main
+
+import "fmt"
+
+func main() {
+	s := "aab"
+	fmt.Println(partition(s))
+}
+
+func partition(s string) [][]string {
+	var res [][]string
+	if len(s) == 0 {
+		return res
+	}
+
+	var backtrack func(s string, path []string, pos int)
+	backtrack = func(s string, path []string, pos int) {
+		if pos == len(s) {
+			tmp := make([]string, len(path))
+			copy(tmp, path)
+			res = append(res, tmp)
+		}
+
+		for i := pos; i < len(s); i++ {
+			if isPalindrome(s[pos : i+1]) {
+				path = append(path, s[pos:i+1])
+				backtrack(s, path, i+1)
+				path = path[:len(path)-1]
+			}
+		}
+	}
+
+	backtrack(s, []string{}, 0)
+
+	return res
+}
+
+func isPalindrome(s string) bool {
+	if len(s) == 0 || len(s) == 1 {
+		return true
+	}
+
+	l := len(s)
+	for i := 0; i < l; i++ {
+		if s[i] != s[l-1] {
+			return false
+		}
+		l--
+	}
+
+	return true
+}

medium/1634_buildTree.go

@@ -0,0 +1,29 @@
+package main
+
+import "fmt"
+
+func main() {
+	preOrder := []int{3, 9, 20, 15, 7}
+	inOrder := []int{9, 3, 15, 20, 7}
+	fmt.Println(buildTree(preOrder, inOrder))
+}
+
+func buildTree(preorder []int, inorder []int) *TreeNode {
+	for i, _ := range inorder {
+		if inorder[i] == preorder[0] {
+			return &TreeNode{
+				Val:   preorder[0],
+				Left:  buildTree(preorder[1:i+1], inorder[:i]),
+				Right: buildTree(preorder[i+1:], inorder[i+1:]),
+			}
+		}
+	}
+
+	return nil
+}
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}

medium/1651_cuttingRope2.go

@@ -0,0 +1,33 @@
+package main
+
+import "fmt"
+
+func main() {
+	n := 120
+	fmt.Println(cuttingRope2(n))
+}
+
+func cuttingRope2(n int) int {
+	var res = 1
+
+	if n <= 3 {
+		return n - 1
+	}
+
+	if n%3 == 1 {
+		res *= 4
+		n -= 4
+	}
+
+	if n%3 == 2 {
+		res *= 2
+		n -= 2
+	}
+
+	for i := 0; i < n/3; i++ {
+		res %= 1e9 + 7
+		res *= 3
+	}
+
+	return res % (1e9 + 7)
+}

medium/1653_myPow.go

@@ -0,0 +1,130 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	x := -13.62608
+	n := 7
+	fmt.Println(myPow(x, n))
+	fmt.Println(myPowIteration(x, n))
+	fmt.Println(myPowSelf(x, n))
+}
+
+// base = x, exponent = n
+func myPow(x float64, n int) float64 {
+	if n == 0 {
+		return 1
+	}
+	if n == 1 {
+		return x
+	}
+
+	if n < 0 {
+		x = 1 / x
+		n = -n
+	}
+
+	res := 1.0
+	for n >= 1 {
+		if n&1 == 1 {
+			res *= x
+			n--
+		} else {
+			res *= x * x
+			n = n >> 1
+		}
+	}
+
+	return res
+}
+
+// base = x, exponent = n
+func myPowIteration(x float64, n int) float64 {
+	if n == 0 {
+		return 1
+	}
+	if n == 1 {
+		return x
+	}
+	if n < 0 {
+		x = 1 / x
+		n = -n
+	}
+
+	temp := myPowIteration(x, n/2)
+	if n%2 == 0 {
+		return temp * temp
+	}
+
+	return temp * temp * x
+}
+
+// base = x, exponent = n
+func myPowSelf(x float64, n int) float64 {
+	var res float64 = 1
+	if x == 1 || n == 0 {
+		return res
+	}
+	if x == 0 {
+		return 0
+	}
+
+	// 判断 x 符号
+	negativeX := false
+	if x < 0 {
+		x = -x
+		negativeX = true
+	}
+
+	// 判断 n 符号
+	negativeN := false
+	if n < 0 {
+		n = -n
+		negativeN = true
+	}
+
+	if n >= math.MaxInt32 {
+		if 0 < x && x < 1 {
+			return 0
+		}
+		if x == 1 && negativeX {
+			if n%2 == 0 {
+				return res
+			}
+			return -res
+		}
+		if x > 1 {
+			if negativeN {
+				return 0
+			}
+
+			// x 为负数
+			if negativeX {
+				if n%2 == 0 {
+					return math.MaxFloat64
+				}
+				return 0
+			}
+			return math.MaxFloat64
+		}
+	}
+
+	for i := 0; i < n; i++ {
+		res *= x
+	}
+
+	if negativeN {
+		res = 1 / res
+	}
+
+	if negativeX {
+		if n%2 != 0 {
+			res = -res
+		}
+	}
+
+	return res
+}

medium/1657_isNumber.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+func main() {
+	s := "3.e5"
+	fmt.Println(isNumber(s))
+}
+
+func isNumber(s string) bool {
+	var res bool
+	s = strings.Trim(s, " ")
+
+	res, _ = regexp.MatchString("^(([+-]?[0-9]+(\\.[0-9]*)?)|([+-]?\\.?[0-9]+))([eE][+-]?[0-9]+)?$", s)
+
+	return res
+}

medium/1682_findNthDigit.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func main() {
+	n := 19
+	fmt.Println(findNthDigit(n))
+}
+
+func findNthDigit(n int) int {
+	// 写法一
+	var start = 1
+	var digit = 1
+	var flag = 9
+
+	for n-flag*digit > 0 {
+		n -= flag * digit
+		flag *= 10
+		start *= 10
+		digit++
+	}
+
+	num := start + (n-1)/digit
+	return int(strconv.Itoa(num)[(n-1)%digit] - '0')
+
+	// 写法二
+	/*digits := 1
+	flag := 9
+	// 求n所在的数为几位数
+	for n-flag*digits > 0 {
+		n = n - flag*digits
+		flag = flag * 10
+		digits++
+	}
+	// 若n为个位数，返回n即可
+	if digits == 1 {
+		return n
+	}
+	number := 1
+	for k := 1; k < digits; k++ {
+		number = number * 10
+	}
+	// 求n对应的数
+	number = number + (n-1)/digits
+	idx := (n - 1) % digits
+	// 将n对应的数转换为字符串类型，取第idx位并转换为整数
+	strnums := strconv.Itoa(number)
+	res, _ := strconv.Atoi(string(strnums[idx]))
+
+	return res*/
+}