'有限状态机'

leetcode/初级算法/字符串/字符串转换整数 (atoi)/有限状态机/main.go

@@ -1,6 +1,69 @@
 package main
 
-import "strings"
+import (
+	"math/big"
+	"strings"
+	"unicode"
+)
+
+var unordered_map = map[string][]string{
+	"start":     {"start", "signed", "in_number", "end"},
+	"signed":    {"end", "end", "in_number", "end"},
+	"in_number": {"end", "end", "in_number", "end"},
+	"end":       {"end", "end", "end", "end"},
+}
+var state = "start"
+
+func get_col(s rune) int {
+	if string(s) == " " {
+		return 0
+	} else if string(s) == "+" || string(s) == "-" {
+		return 1
+	} else if unicode.IsDigit(s) {
+		return 2
+	}
+	return 3
+}
+
+var sign = 1
+
+var ans = big.NewInt(0)
+
+const MIN int64 = -2147483648
+const MAX int64 = 2147483647
+
+func get(s rune) {
+	state = unordered_map[state][get_col(s)]
+	if state == "in_number" {
+		ans.Mul(ans, big.NewInt(10))
+		ans.Add(ans, big.NewInt(int64(s-'0')))
+		if sign == 1 {
+			ans = Max(*ans)
+		} else {
+			ans = Min(*ans)
+		}
+	} else if state == "signed" {
+		if s == '+' {
+			sign = 1
+		} else {
+			sign = -1
+		}
+	}
+}
+
+func Max(a big.Int) *big.Int {
+	if a.Cmp(big.NewInt(MAX)) > 0 {
+		return big.NewInt(MAX)
+	}
+	return &a
+}
+
+func Min(a big.Int) *big.Int {
+	if ans.Cmp(big.NewInt(MIN)) < 0 {
+		return big.NewInt(MIN)
+	}
+	return &a
+}
 
 func myAtoi(s string) int {
 	//去除首尾字符
@@ -8,9 +71,12 @@ func myAtoi(s string) int {
 	if len(s) == 0 {
 		return 0
 	}
-	return 0
+	for _, str := range s {
+		get(str)
+	}
+	return sign * int(ans.Int64())
 }
 
 func main() {
-	print(myAtoi("9223372036854775808"))
+	print(myAtoi("   -42"))
 }