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;}
}