14. Longest Common Prefix
Tags: ‘String’
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: There is no common prefix among the input strings.
Note:
All given inputs are in lowercase letters a-z.
Solution
方法1：Vertical Scanning. Naive solution. 对每个index i 检查所有string，直到i超过某个string长度
O(M*N) O(1) 74% 80%
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];
}
方法2: Horizontal Scanning
LCP(S1...Sn) = LCP...(LCP(LCP(S1, S2), S3)...Sn)
O(M*N) O(1)
public String longestCommonPrefix(String[] strs) {
if (strs == null || strs.length == 0) return "";
String prefix = strs[0];
for (int i = 1; i < strs.length; i++) {
// keep shrinking prefix until match
// if shrink to 0, return
while (strs[i].indexOf(prefix) != 0) {
prefix = prefix.substring(0, prefix.length() - 1);
if (prefix.length() == 0) {
return "";
}
}
}
return prefix;
}
方法3： binary search
方法4： divide and conqur