diff --git a/problems/0139.单词拆分.md b/problems/0139.单词拆分.md index e04cb173..3aa5ca0f 100644 --- a/problems/0139.单词拆分.md +++ b/problems/0139.单词拆分.md @@ -250,30 +250,34 @@ class Solution { // 回溯法+记忆化 class Solution { + private Set set; + private int[] memo; public boolean wordBreak(String s, List wordDict) { - Set wordDictSet = new HashSet(wordDict); - int[] memory = new int[s.length()]; - return backTrack(s, wordDictSet, 0, memory); + memo = new int[s.length()]; + set = new HashSet<>(wordDict); + return backtracking(s, 0); } - - public boolean backTrack(String s, Set wordDictSet, int startIndex, int[] memory) { - // 结束条件 - if (startIndex >= s.length()) { + + public boolean backtracking(String s, int startIndex) { + // System.out.println(startIndex); + if (startIndex == s.length()) { return true; } - if (memory[startIndex] != 0) { - // 此处认为:memory[i] = 1 表示可以拼出i 及以后的字符子串, memory[i] = -1 表示不能 - return memory[startIndex] == 1 ? true : false; + if (memo[startIndex] == -1) { + return false; } - for (int i = startIndex; i < s.length(); ++i) { - // 处理 递归 回溯 循环不变量:[startIndex, i + 1) - String word = s.substring(startIndex, i + 1); - if (wordDictSet.contains(word) && backTrack(s, wordDictSet, i + 1, memory)) { - memory[startIndex] = 1; - return true; + + for (int i = startIndex; i < s.length(); i++) { + String sub = s.substring(startIndex, i + 1); + // 拆分出来的单词无法匹配 + if (!set.contains(sub)) { + continue; } + boolean res = backtracking(s, i + 1); + if (res) return true; } - memory[startIndex] = -1; + // 这里是关键,找遍了startIndex~s.length()也没能完全匹配,标记从startIndex开始不能找到 + memo[startIndex] = -1; return false; } }