最长公共子序列

public int[][] getdp(char[] str1, char[] str2){
   int[][] dp = new int[str1.length][str2.length];
   dp[0][0] = str[0] == str[1] ? 1 : 0;
 for (int i = 1; i < str1.length; i++){
      dp[i][0] = Math.max(dp[i-1][0], str1[i] == str2[0] ? 1 : 0);
 }
    for (int j = 1; i < str2.length; j++){
      dp[0][j] = Math.max(dp[0][j-1], str1[0] == str2[j] ? 1 : 0);
 }
    
 for (int i = 1; i < str1.length; i++){
      for (int j = 1; j < str2.length; j++){
          dp[i][j] = Math.max(dp[i-1][j],dp[i][j-1]);
          if (str1[i] == str2[j]){
                dp[i][j] == Math.max(dp[i][j], dp[i-1][j-1]+1);
          }
        }
    }
    return dp
}
//取出最长公共子序列
public String (String str1, String str2){
 if(str1 == null || str2 == null || str1 == "" || str2 == ""){
     return "";
  }
    
 char[] chs1 = str1.toCharArray();
   char[] chs2 = str2.toCharArray();
   int[][] dp = getdp(chs1, chs2);
 int m = chs1.length -1;
 int n = chs2.length -1;
 char[] res = new char[dp[m][n]];
  int index = res.length -1;
  while(index >= 0){
       if (n > 0 && dp[m][n] == dp[m][n-1]){
            n--;
     }else if(m >0 && dp[m][n] == dp[m-1][n]){
           m--;
     }else{
          res[index--] = chs1[m]
           n--;
         m--;
     }
    }
}