Create 0028-find-the-index-of-the-first-occurrence-in-a-string.kt

kotlin/0028-find-the-index-of-the-first-occurrence-in-a-string.kt

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+/*
+* KMP algorithm
+*/
+class Solution {
+ fun strStr(haystack: String, needle: String): Int {
+ if(needle == "") return 0
+
+ val lps = IntArray(needle.length)
+ var prevLPS = 0
+ var i = 1
+ while(i < needle.length) {
+ if(needle[i] == needle[prevLPS]) {
+ lps[i] = prevLPS + 1
+ prevLPS++
+ i++
+ }else if(prevLPS == 0) {
+ lps[i] = 0
+ i++
+ }else{
+ prevLPS = lps[prevLPS - 1]
+ }
+ }
+
+ i = 0
+ var j = 0
+ while (i < haystack.length) {
+ if(haystack[i] == needle[j]){
+ i++
+ j++
+ }else if(j == 0){
+ i++
+ }else{
+ j = lps[j - 1] 
+ }
+ if(j == needle.length) {
+ return i - needle.length
+ } 
+ }
+
+ return -1
+ }
+}
+
+/*
+* Rabin-Karp string hashing with bad hash
+*/
+class Solution {
+ fun strStr(haystack: String, needle: String): Int {
+ if(needle.length > haystack.length) return -1
+
+ var needleHash = 0
+ var hayHash = 0
+
+ for(i in 0..needle.lastIndex) {
+ needleHash += needle[i] - 'a'
+ hayHash += haystack[i] - 'a'
+ }
+
+ for(i in 0..(haystack.length - needle.length)) {
+ if(hayHash == needleHash) {
+ for(j in 0..needle.lastIndex) {
+ if(haystack[i + j] != needle[j])
+ break
+ if(j == needle.lastIndex)
+ return i
+ }
+ }
+ if(i == haystack.length - needle.length)
+ break
+ hayHash -= haystack[i] - 'a'
+ hayHash += haystack[i + needle.length] - 'a'
+ }
+
+ return -1
+ }
+}
+
+/*
+* Using Trie to match pattern
+*/
+class TrieNode() {
+ val child = arrayOfNulls<TrieNode>(26)
+ var isEnd = false
+}
+
+class Solution {
+ fun strStr(haystack: String, needle: String): Int {
+ if(needle == "") return 0
+
+ var root: TrieNode? = TrieNode()
+
+ var current = root
+ for(c in needle){
+ if(current?.child?.get(c - 'a') == null)
+ current?.child?.set(c - 'a', TrieNode())
+ current = current?.child?.get(c - 'a')
+ }
+ current?.isEnd = true
+
+ var i = 0
+ while(i < haystack.length + 1 - needle.length) {
+ current = root?.child?.get(haystack[i] - 'a')
+ var j = i
+ while(current != null) {
+ if(current.isEnd == true)
+ return i
+ j++
+ if(j - i < needle.length)
+ current = current?.child?.get(haystack[j] - 'a')
+ else
+ break
+ }
+ i++
+ }
+
+ return -1
+ }
+}
+
+/*
+* Brute force 
+*/
+class Solution {
+ fun strStr(haystack: String, needle: String): Int {
+ if(needle == "") return 0
+
+ for(i in 0..(haystack.length - needle.length)) {
+ for(j in 0..needle.lastIndex) {
+ if(haystack[i + j] != needle[j])
+ break
+ if(j == needle.lastIndex)
+ return i
+ }
+ }
+
+ return -1
+ }
+}