[Link] https://www.acmicpc.net/problem/9252
DP solution
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import java.util.*;
import java.io.*;
public class Main {
static BufferedReader br;
static int max = 0, maxIdx = 0;
public static void main(String[] args) throws IOException {
br = new BufferedReader(new InputStreamReader(System.in));
StringBuilder sb = new StringBuilder();
String line1 = br.readLine(), line2 = br.readLine();
int l1 = line1.length(), l2 = line2.length();
int[][] dp = new int[l1][l2]; // dp[i][j]: line1 0 ~ i line 0 ~ j
for(int i = 0; i < l1; i++) {
for(int j = 0; j < l2; j++) {
if(line1.charAt(i) == line2.charAt(j)) {
if(i >= 1 && j >= 1) dp[i][j] = dp[i-1][j-1] + 1;
else dp[i][j] = 1;
} else {
int v1 = i > 0 ? dp[i - 1][j] : 0;
int v2 = j > 0 ? dp[i][j - 1] : 0;
dp[i][j] = Math.max(v1, v2);
}
}
}
println(dp[l1-1][l2-1]);
Stack<Integer> stack = new Stack<>();
int store = dp[l1-1][l2-1];
int ii = l1-1, jj = l2-1;
while(ii >= 0 && jj >=0) {
if(dp[ii][jj] == 0) break;
if(line1.charAt(ii) == line2.charAt(jj)) {
sb.insert(0, line1.charAt(ii));
ii--;
jj--;
continue;
}
int upVal = ii > 0 ? dp[ii-1][jj] : 0;
int preVal = jj > 0 ? dp[ii][jj-1] : 0;
int max = 0;
boolean goUp = true;
if(upVal > preVal) max = upVal;
else {
max = preVal;
goUp = false;
}
if(goUp) ii--;
else jj--;
}
print(sb);
}
static int toi(String s) { return Integer.parseInt(s); }
static String[] getLine() throws IOException { return br.readLine().split(" "); }
static <T> void print(T s) { System.out.print(s); }
static <T> void println(T s) { System.out.println(s); }
}
Time Limit Exceed(Recursive)
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import java.util.*;
import java.io.*;
public class Main {
static BufferedReader br;
static int max = 0, maxIdx = 0;
public static void main(String[] args) throws IOException {
br = new BufferedReader(new InputStreamReader(System.in));
StringBuilder sb = new StringBuilder();
// String[] line = getLine();
String line1 = br.readLine(), line2 = br.readLine();
String[][] dp = new String[line1.length()][line2.length()];
for(String[] tmp : dp) Arrays.fill(tmp, "");
String result = lcs(line1, line2, 0, 0, dp);
if(result.length() == 0) sb.append("0");
else sb.append(result.length()).append("\n").append(result);
print(sb);
}
static String lcs(String line1, String line2, int idx1, int idx2, String[][] dp) {
if(idx1 >= line1.length() || idx2 >= line2.length()) return "";
if(dp[idx1][idx2].length() != 0) return dp[idx1][idx2];
if(line1.charAt(idx1) == line2.charAt(idx2))
return dp[idx1][idx2] = line1.charAt(idx1) + lcs(line1, line2, idx1 + 1, idx2 + 1, dp);
String s1 = lcs(line1, line2, idx1 + 1, idx2, dp), s2 = lcs(line1, line2, idx1, idx2 + 1, dp);
return dp[idx1][idx2] = s1.length() > s2.length() ? s1 : s2;
}
static int toi(String s) { return Integer.parseInt(s); }
static String[] getLine() throws IOException { return br.readLine().split(" "); }
static <T> void print(T s) { System.out.print(s); }
static <T> void println(T s) { System.out.println(s); }
}