LeetCode: 14. Longest Common Prefix

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14. Longest Common Prefix

LeetCode - 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: There is no common prefix among the input strings.

Note:

All given inputs are in lowercase letters a-z.

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/**
 * 使用逐列扫描前进，遇到不同时，则终止。
 *
 * @author D瓜哥 · https://www.diguage.com
 * @since 2019-07-11 17:50
 */
public String longestCommonPrefix(String[] strs) {
  if (Objects.isNull(strs) || 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];
}

public String longestCommonPrefix2(String[] strs) {
  if (Objects.isNull(strs) || strs.length == 0) {
    return "";
  }
  if (strs.length == 1) {
    return strs[0];
  }
  int maxLength = Integer.MAX_VALUE;
  for (String str : strs) {
    int strLength = str.length();
    if (strLength < maxLength) {
      maxLength = strLength;
    }
  }

  int length = 0;

  loop:
  while (length < maxLength) {
    char aChar = strs[0].charAt(length);
    for (int i = 1; i < strs.length; i++) {
      char bChar = strs[i].charAt(length);
      if (aChar != bChar) {
        break loop;
      }
    }
    length += 1;
  }
  if (length > 0) {
    return strs[0].substring(0, length);
  } else {
    return "";
  }
}