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ImplementstrStr().java
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78 lines (76 loc) · 2.71 KB
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/*
Author: King, wangjingui@outlook.com
Date: Dec 17, 2014
Problem: Implement strStr()
Difficulty: Easy
Source: https://oj.leetcode.com/problems/implement-strstr/
Notes:
Implement strStr().
Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.
Solution: 1. Check in the haystack one by one. If not equal to needle, reset the pointer.(TLE)
2. Classice KMP solution.
3. Simplified RK Soluiton. Thanks for [wenyuanhust, wenyuanhust@gmail.com]
*/
public class Solution {
public int strStr_1(String haystack, String needle) {
int sLen = haystack.length(), tLen = needle.length();
if(tLen == 0) return 0;
if (haystack==null || needle==null || sLen==0) return -1;
int i = 0, j = 0;
while (i < sLen) {
for (j = 0; j < tLen && (i+j) < sLen && haystack.charAt(i+j) == needle.charAt(j); ++j);
if (j == tLen) return i;
++i;
}
return (int)-1;
}
void getNext(String T, int[] next){
int i=0, j=-1;
next[0]=-1;
int n = next.length;
while(i < n - 1){
while(j>-1&&T.charAt(j)!=T.charAt(i)) j = next[j];
++i; ++j;
if(i < n - 1 && j < n - 1 && T.charAt(j)==T.charAt(i)) next[i]=next[j];
else next[i]=j;
}
}
public int strStr_2(String haystack, String needle) {
int sLen = haystack.length(), tLen = needle.length();
if(tLen == 0) return 0;
if (haystack==null || needle==null || sLen==0) return -1;
int[] next = new int[tLen+1];
getNext(needle, next);
int i = 0, j = 0;
while (i < sLen) {
while (j > -1 && needle.charAt(j) != haystack.charAt(i)) j = next[j];
++i; ++j;
if (j == tLen) return i - j;
}
return -1;
}
public int strStr_3(String haystack, String needle) {
int sLen = haystack.length(), tLen = needle.length();
if (tLen == 0) return 0;
if (haystack==null || needle==null || sLen==0 || sLen < tLen) return -1;
long fh = 0, fn = 0;
int head = 0, tail = tLen - 1;
for (int i = 0; i < tLen; ++i) {
fh += haystack.charAt(i);
fn += needle.charAt(i);
}
while (tail < sLen) {
if (fn == fh) {
int i = 0;
while (i < tLen && needle.charAt(i) == haystack.charAt(i + head)){
++i;
}
if (i == tLen) return head;
}
if (tail == sLen - 1) return -1;
fh -= haystack.charAt(head++);
fh += haystack.charAt(++tail);
}
return -1;
}
}