Merge pull request #139 from NovaHe/fix/91

Fix/91 and 80

Author: halfrost

leetcode/0080.Remove-Duplicates-from-Sorted-Array-II/80. Remove Duplicates from Sorted Array II.go

@@ -1,35 +1,12 @@
 package leetcode
 
-func removeDuplicates80(nums []int) int {
-	if len(nums) == 0 {
-		return 0
-	}
-	last, finder := 0, 0
-	for last < len(nums)-1 {
-		startFinder := -1
-		for nums[finder] == nums[last] {
-			if startFinder == -1 || startFinder > finder {
-				startFinder = finder
-			}
-			if finder == len(nums)-1 {
-				break
-			}
-			finder++
-		}
-		if finder-startFinder >= 2 && nums[finder-1] == nums[last] && nums[finder] != nums[last] {
-			nums[last+1] = nums[finder-1]
-			nums[last+2] = nums[finder]
-			last += 2
-		} else {
-			nums[last+1] = nums[finder]
-			last++
-		}
-		if finder == len(nums)-1 {
-			if nums[finder] != nums[last-1] {
-				nums[last] = nums[finder]
-			}
-			return last + 1
+func removeDuplicates(nums []int) int {
+	slow := 0
+	for fast, v := range nums {
+		if fast < 2 || nums[slow-2] != v {
+			nums[slow] = v
+			slow++
 		}
 	}
-	return last + 1
+	return slow
 }

leetcode/0080.Remove-Duplicates-from-Sorted-Array-II/80. Remove Duplicates from Sorted Array II_test.go

@@ -61,7 +61,7 @@ func Test_Problem80(t *testing.T) {
 
 	for _, q := range qs {
 		_, p := q.ans80, q.para80
-		fmt.Printf("【input】:%v    【output】:%v\n", p.one, removeDuplicates80(p.one))
+		fmt.Printf("【input】:%v    【output】:%v\n", p.one, removeDuplicates(p.one))
 	}
 	fmt.Printf("\n\n\n")
 }

leetcode/0080.Remove-Duplicates-from-Sorted-Array-II/README.md

@@ -51,6 +51,6 @@ for (int i = 0; i < len; i++) {
 
 ## 解题思路
 
-这道题和第 26 题很像。是第 26 题的加强版。这道题和第 283 题，第 27 题基本一致，283 题是删除 0，27 题是删除指定元素，这一题是删除重复元素，实质是一样的。
-
-这里数组的删除并不是真的删除，只是将删除的元素移动到数组后面的空间内，然后返回数组实际剩余的元素个数，OJ 最终判断题目的时候会读取数组剩余个数的元素进行输出。
+问题提示有序数组，一般最容易想到使用双指针的解法，双指针的关键点：移动两个指针的条件。
+在该题中移动的条件：快指针从头遍历数组，慢指针指向修改后的数组的末端，当慢指针指向倒数第二个数与快指针指向的数不相等时，才移动慢指针，同时赋值慢指针
+处理边界条件：当数组小于两个元素时，不做处理

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/0001~0099/0080.Remove-Duplicates-from-Sorted-Array-II.md

@@ -2,9 +2,11 @@
 
 ## 题目
 
-Given a sorted array nums, remove the duplicates in-place such that duplicates appeared at most twice and return the new length.
+Given a sorted array nums, remove the duplicates in-place such that duplicates appeared at most twice and return the new
+length.
 
-Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
+Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra
+memory.
 
 **Example 1**:
 
@@ -34,7 +36,8 @@ It doesn't matter what values are set beyond the returned length.
 
 Confused why the returned value is an integer but your answer is an array?
 
-Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.
+Note that the input array is passed in by reference, which means modification to the input array will be known to the
+caller as well.
 
 Internally you can think of this:
 
@@ -67,44 +70,20 @@ for (int i = 0; i < len; i++) {
 
 package leetcode
 
-func removeDuplicates80(nums []int) int {
-	if len(nums) == 0 {
-		return 0
-	}
-	last, finder := 0, 0
-	for last < len(nums)-1 {
-		startFinder := -1
-		for nums[finder] == nums[last] {
-			if startFinder == -1 || startFinder > finder {
-				startFinder = finder
-			}
-			if finder == len(nums)-1 {
-				break
-			}
-			finder++
-		}
-		if finder-startFinder >= 2 && nums[finder-1] == nums[last] && nums[finder] != nums[last] {
-			nums[last+1] = nums[finder-1]
-			nums[last+2] = nums[finder]
-			last += 2
-		} else {
-			nums[last+1] = nums[finder]
-			last++
-		}
-		if finder == len(nums)-1 {
-			if nums[finder] != nums[last-1] {
-				nums[last] = nums[finder]
-			}
-			return last + 1
+func removeDuplicates(nums []int) int {
+	slow := 0
+	for fast, v := range nums {
+		if fast < 2 || nums[slow-2] != v {
+			nums[slow] = v
+			slow++
 		}
 	}
-	return last + 1
+	return slow
 }
 
 
 ```
 
-
 ----------------------------------------------
 <div style="display: flex;justify-content: space-between;align-items: center;">
 <p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0079.Word-Search/">⬅️上一页</a></p>

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]
 }
 
 ```