题目：

题解：

class Solution {
    public String findLongestWord(String s, List<String> dictionary) {
        int m = s.length();
        int[][] f = new int[m + 1][26];
        Arrays.fill(f[m], m);

        for (int i = m - 1; i >= 0; --i) {
            for (int j = 0; j < 26; ++j) {
                if (s.charAt(i) == (char) ('a' + j)) {
                    f[i][j] = i;
                } else {
                    f[i][j] = f[i + 1][j];
                }
            }
        }
        String res = "";
        for (String t : dictionary) {
            boolean match = true;
            int j = 0;
            for (int i = 0; i < t.length(); ++i) {
                if (f[j][t.charAt(i) - 'a'] == m) {
                    match = false;
                    break;
                }
                j = f[j][t.charAt(i) - 'a'] + 1;
            }
            if (match) {
                if (t.length() > res.length() ||  (t.length() == res.length() && t.compareTo(res) < 0)) {
                    res = t;
                }
            }
        }
        return res;
    }
}