目录

335. 路径交叉 Self-crossing  🌟🌟🌟

336. 回文对 Palindrome Pairs  🌟🌟🌟

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335. 路径交叉 Self-crossing

给你一个整数数组 distance 。

从 X-Y 平面上的点 (0,0) 开始，先向北移动 distance[0] 米，然后向西移动 distance[1] 米，向南移动 distance[2] 米，向东移动 distance[3] 米，持续移动。也就是说，每次移动后你的方位会发生逆时针变化。

判断你所经过的路径是否相交。如果相交，返回 true ；否则，返回 false 。

示例 1：

输入：distance = [2,1,1,2]
输出：true

示例 2：

输入：distance = [1,2,3,4]
输出：false

示例 3：

输入：distance = [1,1,1,1]
输出：true

提示：

• 1 <= distance.length <= 10^5
• 1 <= distance[i] <= 10^5

代码：

package mainimport "fmt"func isSelfCrossing(distance []int) bool {n := len(distance)if n <= 3 {return false}for i := 3; i < n; i++ {// 第四条边与第一条边相交if distance[i] >= distance[i-2] && distance[i-1] <= distance[i-3] {return true}// 第五条边与第一条边重叠或者相交if i >= 4 && distance[i-1] == distance[i-3] && distance[i]+distance[i-4] >= distance[i-2] {return true}// 第六条边与第一条边相交if i >= 5 && distance[i-2]-distance[i-4] >= 0 && distance[i]+distance[i-4] >= distance[i-2] && distance[i-1]-distance[i-3] >= 0 && distance[i-1]-distance[i-3] <= distance[i-5] && distance[i-2]-distance[i-4] <= distance[i-1]-distance[i-3] {return true}}return false
}func main() {distance := []int{2,1,1,2}fmt.Println(isSelfCrossing(distance ))distance = []int{1,2,3,4}fmt.Println(isSelfCrossing(distance ))distance = []int{1,1,1,1}fmt.Println(isSelfCrossing(distance ))
}

输出：

true
false
true

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336. 回文对 Palindrome Pairs

给定一组 互不相同 的单词， 找出所有 不同 的索引对 (i, j)，使得列表中的两个单词， words[i] + words[j] ，可拼接成回文串。

示例 1：

输入：words = ["abcd","dcba","lls","s","sssll"]
输出：[[0,1],[1,0],[3,2],[2,4]] 
解释：可拼接成的回文串为 ["dcbaabcd","abcddcba","slls","llssssll"]

示例 2：

输入：words = ["bat","tab","cat"]
输出：[[0,1],[1,0]] 
解释：可拼接成的回文串为 ["battab","tabbat"]

示例 3：

输入：words = ["a",""]
输出：[[0,1],[1,0]]

提示：

• 1 <= words.length <= 5000
• 0 <= words[i].length <= 300
• words[i] 由小写英文字母组成

代码：

package mainimport "fmt"func palindromePairs(words []string) [][]int {res := [][]int{}wordIndexMap := map[string]int{}for i, word := range words {wordIndexMap[word] = i}for i, word := range words {for j := 0; j <= len(word); j++ {prefix := word[:j]suffix := word[j:]if isPalindrome(prefix) {reverseSuffix := reverseString(suffix)if idx, ok := wordIndexMap[reverseSuffix]; ok && idx != i {res = append(res, []int{idx, i})}}if isPalindrome(suffix) {reversePrefix := reverseString(prefix)if idx, ok := wordIndexMap[reversePrefix]; ok && idx != i && len(suffix) > 0 {res = append(res, []int{i, idx})}}}}return res
}func isPalindrome(s string) bool {i, j := 0, len(s)-1for i < j {if s[i] != s[j] {return false}i++j--}return true
}func reverseString(s string) string {res := ""for i := len(s) - 1; i >= 0; i-- {res += string(s[i])}return res
}func main() {words := []string{"abcd","dcba","lls","s","sssll"}fmt.Println(palindromePairs(words))words = []string{"bat","tab","cat"}fmt.Println(palindromePairs(words))words = []string{"a", ""}fmt.Println(palindromePairs(words))
}

输出：

[[1 0] [0 1] [3 2] [2 4]]

[[1 0] [0 1]]

[[0 1] [1 0]]

暴力循环：

package mainimport "fmt"func palindromePairs(words []string) [][]int {res := [][]int{}for i := 0; i < len(words); i++ {for j := i + 1; j < len(words); j++ {if isPalindrome(words[i] + words[j]) {res = append(res, []int{i, j})}if isPalindrome(words[j] + words[i]) {res = append(res, []int{j, i})}}}return res
}func isPalindrome(s string) bool {i, j := 0, len(s)-1for i < j {if s[i] != s[j] {return false}i++j--}return true
}func main() {words := []string{"abcd","dcba","lls","s","sssll"}fmt.Println(palindromePairs(words))// 输出: [[0 1] [1 0] [3 2] [2 4]]words = []string{"bat","tab","cat"}fmt.Println(palindromePairs(words))// 输出: [[0 1] [1 0]]words = []string{"a", ""}fmt.Println(palindromePairs(words))// 输出: [[0 1] [1 0]]
}

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