最长公共序列

最长公共序列

public class Solution {
    /**
     * longest common subsequence
     * @param s1 string字符串 the string
     * @param s2 string字符串 the string
     * @return string字符串
     */
    public String LCS (String s1, String s2) {
        // write code here
        int len1 = s1.length(), len2 = s2.length();
        if(len1==0 || len2==0){
            return "-1";
        }
        int[][] dp = new int[len1+1][len2+1];
        for (int i = 0; i < len1+1; i++) {
            for (int j = 0; j < len2+1; j++) {
                if(i==0 || j==0){
                    dp[i][j] = 0;
                }else if(s1.charAt(i-1)==s2.charAt(j-1)){
                    dp[i][j] = dp[i-1][j-1]+1;
                }else {
                    dp[i][j] = Math.max(dp[i][j-1],dp[i-1][j]);
                }
            }
        }
        StringBuilder sb = new StringBuilder();
        int sl1 = len1, sl2 = len2;
        while (sl1>0 && sl2>0){
            if(s1.charAt(sl1-1)==s2.charAt(sl2-1)){
                sl1--;
                sl2--;
                sb.append(s1.charAt(sl1));
            }else{
                if(dp[sl1-1][sl2]>dp[sl1][sl2-1]){
                    sl1--;
                }else {
                    sl2--;
                }
            }
        }
        if(sb.length()==0){
            return "-1";
        }
        return sb.reverse().toString();
        
    }
}