leetcode-14.最长公共前缀(图)

Posted 2021-09-13 自行车在路上

文章目录

• leetcode-14.最长公共前缀
• 图-思路
• • 图-横向扫描
  • 图-纵向扫描
  • 图-分治
  • 图-二分查找
• 代码
• • 代码-横向扫描
  • 代码-纵向扫描
  • 代码-分治
  • 代码-二分查找
• demo下载路径
• 参考

leetcode-14.最长公共前缀

编写一个函数来查找字符串数组中的最长公共前缀。

如果不存在公共前缀，返回空字符串 ""。

 

示例 1：

输入：strs = ["flower","flow","flight"]
输出："fl"

示例 2：

输入：strs = ["dog","racecar","car"]
输出：""
解释：输入不存在公共前缀。

 

提示：

• 1 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] 仅由小写英文字母组成

图-思路

图-横向扫描

图-纵向扫描

图-分治

图-二分查找

代码

代码-横向扫描

package com.example.demo.algorithm;

import org.junit.Assert;
import org.junit.Test;

/**
 * @description：最长公共前缀 横向扫描
 */
public class LeetCode14LongestCommonPrefix {

    @Test
    public void test1() {
        LeetCode14LongestCommonPrefix palindromeNumber = new LeetCode14LongestCommonPrefix();
        String[] inputs = new String[]{"ab","abc","abcd"};
        String result = palindromeNumber.longestCommonPrefix(inputs);
        Assert.assertEquals("ab", result);

    }

    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";
        }
        String prefix = strs[0];
        int count = strs.length;
        for (int i = 1; i < count; i++) {
            prefix = longestCommonPrefix(prefix, strs[i]);
            if (prefix.length() == 0) {
                break;
            }
        }
        return prefix;
    }

    public String longestCommonPrefix(String str1, String str2) {
        int length = Math.min(str1.length(), str2.length());
        int index = 0;
        while (index < length && str1.charAt(index) == str2.charAt(index)) {
            index++;
        }
        return str1.substring(0, index);
    }
}

代码-纵向扫描

package com.example.demo.algorithm;

import org.junit.Assert;
import org.junit.Test;

/**
 * @description：最长公共前缀 纵向扫描
 */
public class LeetCode14LongestCommonPrefix2 {

    @Test
    public void test1() {
        LeetCode14LongestCommonPrefix2 palindromeNumber = new LeetCode14LongestCommonPrefix2();
        String[] inputs = new String[]{"ab","abc","abcd"};
        String result = palindromeNumber.longestCommonPrefix(inputs);
        Assert.assertEquals("ab", result);

    }

    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";
        }
        int length = strs[0].length();
        int count = strs.length;
        for (int i = 0; i < length; i++) {
            char c = strs[0].charAt(i);
            for (int j = 1; j < count; j++) {
                if (i == strs[j].length() || strs[j].charAt(i) != c) {
                    return strs[0].substring(0, i);
                }
            }
        }
        return strs[0];
    }
}

代码-分治

package com.example.demo.algorithm;

import org.junit.Assert;
import org.junit.Test;

/**
 * @description：最长公共前缀 分治
 */
public class LeetCode14LongestCommonPrefix3 {

    @Test
    public void test1() {
        LeetCode14LongestCommonPrefix3 palindromeNumber = new LeetCode14LongestCommonPrefix3();
        String[] inputs = new String[]{"ab","abc","abcd"};
        String result = palindromeNumber.longestCommonPrefix(inputs);
        Assert.assertEquals("ab", result);

    }

    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";
        } else {
            return longestCommonPrefix(strs, 0, strs.length - 1);
        }
    }

    public String longestCommonPrefix(String[] strs, int start, int end) {
        if (start == end) {
            return strs[start];
        } else {
            int mid = (end - start) / 2 + start;
            String lcpLeft = longestCommonPrefix(strs, start, mid);
            String lcpRight = longestCommonPrefix(strs, mid + 1, end);
            return commonPrefix(lcpLeft, lcpRight);
        }
    }

    public String commonPrefix(String lcpLeft, String lcpRight) {
        int minLength = Math.min(lcpLeft.length(), lcpRight.length());
        for (int i = 0; i < minLength; i++) {
            if (lcpLeft.charAt(i) != lcpRight.charAt(i)) {
                return lcpLeft.substring(0, i);
            }
        }
        return lcpLeft.substring(0, minLength);
    }

//    作者：LeetCode-Solution
//    链接：https://leetcode-cn.com/problems/longest-common-prefix/solution/zui-chang-gong-gong-qian-zhui-by-leetcode-solution/
//    来源：力扣（LeetCode）
//    著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。
}

代码-二分查找

package com.example.demo.algorithm;

import org.junit.Assert;
import org.junit.Test;

/**
 * @description：最长公共前缀 二分查找
 */
public class LeetCode14LongestCommonPrefix4 {

    @Test
    public void test1() {
        LeetCode14LongestCommonPrefix4 palindromeNumber = new LeetCode14LongestCommonPrefix4();
        String[] inputs = new String[]{"ab","abc","abcd"};
        String result = palindromeNumber.longestCommonPrefix(inputs);
        Assert.assertEquals("ab", result);

    }

    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";
        }
        int minLength = Integer.MAX_VALUE;
        for (String str : strs) {
            minLength = Math.min(minLength, str.length());
        }
        int low = 0, high = minLength;
        while (low < high) {
            int mid = (high - low + 1) / 2 + low;
            if (isCommonPrefix(strs, mid)) {
                low = mid;
            } else {
                high = mid - 1;
            }
        }
        return strs[0].substring(0, low);
    }

    public boolean isCommonPrefix(String[] strs, int length) {
        String str0 = strs[0].substring(0, length);
        int count = strs.length;
        for (int i = 1; i < count; i++) {
            String str = strs[i];
            for (int j = 0; j < length; j++) {
                if (str0.charAt(j) != str.charAt(j)) {
                    return false;
                }
            }
        }
        return true;
    }

//    作者：LeetCode-Solution
//    链接：https://leetcode-cn.com/problems/longest-common-prefix/solution/zui-chang-gong-gong-qian-zhui-by-leetcode-solution/
//    来源：力扣（LeetCode）
//    著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。
}

demo下载路径

码云

参考

出处

14.最长公共前缀