update 91

Author: novahe

leetcode/0091.Decode-Ways/91. Decode Ways.go

@@ -1,29 +1,16 @@
 package leetcode
 
-import (
-	"strconv"
-)
-
 func numDecodings(s string) int {
-	if len(s) == 0 {
-		return 0
-	}
-	dp := make([]int, len(s)+1)
+	n := len(s)
+	dp := make([]int, n+1)
 	dp[0] = 1
-	if s[:1] == "0" {
-		dp[1] = 0
-	} else {
-		dp[1] = 1
-	}
-	for i := 2; i <= len(s); i++ {
-		lastNum, _ := strconv.Atoi(s[i-1 : i])
-		if lastNum >= 1 && lastNum <= 9 {
+	for i := 1; i <= n; i++ {
+		if s[i-1] != '0' {
 			dp[i] += dp[i-1]
 		}
-		lastNum, _ = strconv.Atoi(s[i-2 : i])
-		if lastNum >= 10 && lastNum <= 26 {
+		if i > 1 && s[i-2] != '0' && (s[i-2]-'0')*10+(s[i-1]-'0') <= 26 {
 			dp[i] += dp[i-2]
 		}
 	}
-	return dp[len(s)]
+	return dp[n]
 }

website/content/ChapterFour/0001~0099/0091.Decode-Ways.md

@@ -51,32 +51,19 @@ Given a **non-empty** string containing only digits, determine the total numbe
 
 package leetcode
 
-import (
-	"strconv"
-)
-
 func numDecodings(s string) int {
-	if len(s) == 0 {
-		return 0
-	}
-	dp := make([]int, len(s)+1)
+	n := len(s)
+	dp := make([]int, n+1)
 	dp[0] = 1
-	if s[:1] == "0" {
-		dp[1] = 0
-	} else {
-		dp[1] = 1
-	}
-	for i := 2; i <= len(s); i++ {
-		lastNum, _ := strconv.Atoi(s[i-1 : i])
-		if lastNum >= 1 && lastNum <= 9 {
+	for i := 1; i <= n; i++ {
+		if s[i-1] != '0' {
 			dp[i] += dp[i-1]
 		}
-		lastNum, _ = strconv.Atoi(s[i-2 : i])
-		if lastNum >= 10 && lastNum <= 26 {
+		if i > 1 && s[i-2] != '0' && (s[i-2]-'0')*10+(s[i-1]-'0') <= 26 {
 			dp[i] += dp[i-2]
 		}
 	}
-	return dp[len(s)]
+	return dp[n]
 }
 
 ```