java显示最长共同前缀_Java 算法-最长公共前缀(字典树)
今天lintCode上面做了一道面试题，这道题不难，但是就是有多种的解法，所以觉得有必要记录下来，主要是这道题有字典树的解法~~~字典树相对另一种解法，复杂度没有明显的改善，这里只是为了记录多种方法。
1.概览
(1).题意
给k个字符串，求出他们的最长公共前缀(LCP)
(2).样例
在 "ABCD" "ABEF" 和 "ACEF" 中, LCP 为 "A"
在 "ABCDEFG", "ABCEFG", "ABCEFA" 中, LCP 为 "ABC"
2.代码
由于这道题非常的简单，就不用解释解题思路，最简单的方法就是暴力。
(1).传统解法--暴力法
public String longestCommonPrefix(String[] strs) {
int minLength = Integer.MAX_VALUE;
String minLengthString = null;
for (int i = 0; i < strs.length; i++) {
if (minLength > strs[i].length()) {
minLength = strs[i].length();
minLengthString = strs[i];
}
}
for (int i = minLength; i >= 0; i--) {
String string = minLengthString.substring(0, i);
int j = 0;
for (j = 0; j < strs.length; j++) {
if(!string.equals(strs[j].substring(0, i))) {
break;
}
}
if(j == strs.length) {
return string;
}
}
return "";
}
(2).字典树
public class Solution {
/*
* @param strs: A list of strings
* @return: The longest common prefix
*/
public String longestCommonPrefix(String[] strs) {
for(int i = 0; i < strs.length; i++) {
if(strs[i].equals("")) {
return "";
}
}
DictionaryTree dictionaryTree = new DictionaryTree();
for(int i = 0; i < strs.length; i++) {
dictionaryTree.addWord(strs[i]);
}
return dictionaryTree.longestCommonPrefix();
}
}
class DictionaryTree {
TreeNode root;
public DictionaryTree() {
root = new TreeNode(' ');
}
public void addWord(String word) {
TreeNode node = root;
for(int i = 0; i < word.length(); i++) {
if(!node.map.containsKey(word.charAt(i))) {
node.map.put(word.charAt(i), new TreeNode(word.charAt(i)));
node.len++;
node.c = word.charAt(i);
}
node = node.map.get(word.charAt(i));
}
}
public String longestCommonPrefix() {
StringBuilder stringBuilder = new StringBuilder("");
TreeNode node = root;
while(node.len == 1) {
stringBuilder.append(node.c);
node = node.map.get(node.c);
}
return stringBuilder.toString();
}
private class TreeNode{
char value;
Map map = null;
int len = 0;
char c = ' ';
public TreeNode(char value) {
this.value = value;
map = new HashMap<>();
}
}
}