题目
https://leetcode-cn.com/problems/longest-common-prefix
解法
两个比较
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| class Solution {
public String longestCommonPrefix(String[] strs) {
if (strs == null || strs.length == 0) {
return "";
}
int len = strs.length;
String prefix = strs[0];
for (int i=1; i<len; i++) {
int minLen = Math.min(prefix.length(), strs[i].length());
StringBuilder stringBuilder = new StringBuilder();
for (int j=0; j<minLen; j++) {
if (prefix.charAt(j) == strs[i].charAt(j)) {
stringBuilder.append(prefix.charAt(j));
} else {
break;
}
prefix = stringBuilder.toString();
}
if (prefix.length() ==0) {
break;
}
}
return prefix;
}
class Solution {
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);
}
}
|
横向扫描
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| class Solution {
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];
}
}
|
方法四：二分查找
显然，最长公共前缀的长度不会超过字符串数组中的最短字符串的长度。用 minLength 表示字符串数组中的最短字符串的长度，则可以在[0,minLength] 的范围内通过二分查找得到最长公共前缀的长度。每次取查找范围的中间值mid，判断每个字符串的长度为mid 的前缀是否相同，如果相同则最长公共前缀的长度一定大于或等于 mid，如果不相同则最长公共前缀的长度一定小于mid，通过上述方式将查找范围缩小一半，直到得到最长公共前缀的长度。
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| class Solution {
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;
}
}
|
