Longest Common Subsequence
Given two strings, find the longest common subsequence (LCS).
Your code should return the length of LCS.
Example
Example 1:
Input: "ABCD" and "EDCA"
Output: 1
Explanation:
LCS is 'A' or 'D' or 'C'
Example 2:
Input: "ABCD" and "EACB"
Output: 2
Explanation:
LCS is "AC"
Note
if (A.charAt(i - 1) == B.charAt(j - 1)) {
dp[i][j] = dp[i - 1][j - 1] + 1;
} else {
dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
}
Code
public class Solution {
/**
* @param A: A string
* @param B: A string
* @return: The length of longest common subsequence of A and B
*/
public int longestCommonSubsequence(String A, String B) {
// write your code here
if (A == null || B == null || A.length() == 0 || B.length() == 0) {
return 0;
}
int m = A.length();
int n = B.length();
int[][] dp = new int[n + 1][m + 1];
for (int i = 1; i <= m; i++) {
for (int j = 1; j <= n; j++) {
if (A.charAt(i - 1) == B.charAt(j - 1)) {
dp[i][j] = dp[i - 1][j - 1] + 1;
} else {
dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
}
}
}
return dp[m][n];
}
}
public class Solution {
/**
* @param A: A string
* @param B: A string
* @return: The length of longest common subsequence of A and B
*/
public int longestCommonSubsequence(String A, String B) {
// write your code here
if (A.isEmpty() || B.isEmpty()) {
return 0;
}
int m = A.length();
int n = B.length();
int[][] memo = new int[m+1][n+1];
for (int i = 0; i <= m; i++) {
Arrays.fill(memo[i], -1);
}
return dfs(A, B, memo, m, n);
}
private int dfs(String A, String B, int[][] memo, int m, int n) {
if (memo[m][n] != -1) {
return memo[m][n];
}
int result = 0;
if (m == 0 || n == 0) {
result = 0;
} else if (A.charAt(m-1) == B.charAt(n-1)) {
result = dfs(A, B, memo, m-1, n-1) + 1;
} else {
result = Math.max(dfs(A, B, memo, m, n-1), dfs(A, B, memo, m-1, n));
}
memo[m][n] = result;
return result;
}
}
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