Leetcode 之 Longest Common Prefix
阿新 • • 發佈:2018-12-04
Longest Common Prefix
Write a function to find the longest common prefix string amongst an array of strings.
If there is no common prefix, return an empty string ""
.
Example 1:
Input: [“flower”,“flow”,“flight”]
Output: “fl”
Example 2:
Input: [“dog”,“racecar”,“car”]
Output: “”
Explanation:
Note:
All given inputs are in lowercase letters a-z
.
Answer1 基於遍歷的演算法:
class Solution { public String longestCommonPrefix(String[] strs) { if (strs == null || strs.length == 0) return ""; for (int i = 0; i < strs[0].length() ; i++){ char c = strs[0].charAt(i); for (int j = 1; j < strs.length; j ++) { if (i == strs[j].length() || strs[j].charAt(i) != c) return strs[0].substring(0, i); } } return strs[0]; } }
Answer2 基於剪下匹配串的演算法
class Solution { public String longestCommonPrefix(String[] strs) { if(strs.length == 0) { return ""; } String prefix = strs[0]; for (int i = 1; i < strs.length; i++) { while (strs[i].indexOf(prefix) != 0) { prefix = prefix.substring(0, prefix.length() - 1); } } if (prefix.equals("")) { return ""; } return prefix; } }
Answer3 基於分治與遞迴的演算法
class Solution {
public String longestCommonPrefix(String[] strs) {
if(strs.length == 0 ||strs == null){
return "";
}
return longComPredix(strs,0,strs.length-1);
}
public String longComPredix(String[] strs, int l , int r){
if(l==r){
return strs[l];
}else {
int m = (l+r)/2;
String lStr = longComPredix(strs,l,m);
String rStr = longComPredix(strs,m+1,r);
return longComPredix(lStr,rStr);
}
}
public String longComPredix(String str1,String str2){
if(str1.length()==0 || str2.length()==0){
return "";
}
int min = Math.min(str1.length(),str2.length());
for(int i = 0;i<min;i++){
if(str1.charAt(i)!=str2.charAt(i)){
return str1.substring(0,i);
}
}
return str1.substring(0,min);
}
}