LCS (Longest Common Subsquence/String)
子序列
子串
最長子序列
| 代碼如下 |
複製代碼 |
public static int getLongestCommonSubsequence(String a, String b){
int m = a.length();
int n = b.length();
int[][] dp = new int[m+1][n+1]; for(int i=0; i<=m; i++){
for(int j=0; j<=n; j++){
if(i==0 || j==0){
dp[i][j]=0;
}else if(a.charAt(i-1)==b.charAt(j-1)){
dp[i][j] = 1 + dp[i-1][j-1];
}else{
dp[i][j] = Math.max(dp[i-1][j], dp[i][j-1]);
}
}
} return dp[m][n];
} |
最長子串
輸出最長長度
| 代碼如下 |
複製代碼 |
public static int longestSubstr(String first, String second) {
if (first == null || second == null || first.length() == 0
|| second.length() == 0) {
return 0;
} int maxLen = 0;
int fl = first.length();
int sl = second.length();
int[][] table = new int[fl + 1][sl + 1]; for (int i = 1; i <= fl; i++) {
for (int j = 1; j <= sl; j++) {
if (first.charAt(i - 1) == second.charAt(j - 1)) {
if (i == 1 || j == 1) {
table[i][j] = 1;
} else {
table[i][j] = table[i - 1][j - 1] + 1;
}
if (table[i][j] > maxLen) {
maxLen = table[i][j];
}
}
}
}
return maxLen;
} |
輸出最長子串
| 代碼如下 |
複製代碼 |
public static String longestSubstring(String str1, String str2) {
StringBuilder sb = new StringBuilder();
if (str1 == null || str1.isEmpty() || str2 == null || str2.isEmpty())
return ""; // ignore case
str1 = str1.toLowerCase();
str2 = str2.toLowerCase(); // java initializes them already with 0
int[][] num = new int[str1.length()][str2.length()];
int maxlen = 0;
int lastSubsBegin = 0; for (int i = 0; i < str1.length(); i++) {
for (int j = 0; j < str2.length(); j++) {
if (str1.charAt(i) == str2.charAt(j)) {
if ((i == 0) || (j == 0))
num[i][j] = 1;
else
num[i][j] = 1 + num[i - 1][j - 1]; if (num[i][j] > maxlen) {
maxlen = num[i][j];
// generate substring from str1 => i
int thisSubsBegin = i - num[i][j] + 1;
if (lastSubsBegin == thisSubsBegin) {
// if the current LCS is the same as the last time
// this block ran
sb.append(str1.charAt(i));
} else {
// this block resets the string builder if a
// different LCS is found
lastSubsBegin = thisSubsBegin;
sb = new StringBuilder();
sb.append(str1.substring(lastSubsBegin, i + 1));
}
}
}
}
} return sb.toString();
} |
