图 DFS BFS 回溯

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#1 图的遍历

DFS：先序也可后序，就是无法中序。递归，非递归

https://oj.leetcode.com/tag/depth-first-search/

BFS：层序。只能递归。好处是容易找最短路径。

https://oj.leetcode.com/tag/breadth-first-search/

图：因为有环，所以需要判断是否访问过。

https://oj.leetcode.com/tag/graph/

Backtracking：根据条件，提前终止某些分支的遍历。

https://oj.leetcode.com/tag/backtracking/

D1： https://oj.leetcode.com/problems/clone-graph/ （BFS/DFS）

E12：https://oj.leetcode.com/problems/copy-list-with-random-pointer/ （使用map不是最好办法）

D2：https://oj.leetcode.com/problems/word-ladder/ (BFS)

https://oj.leetcode.com/problems/word-ladder-ii/ (BFS + DFS)

D3：https://oj.leetcode.com/problems/word-search/ (DFS backtracking) （重）

D4：https://oj.leetcode.com/problems/word-break/ (DFS + Mem 或者DP)

https://oj.leetcode.com/problems/word-break-ii/ (DFS + Mem)

D8：https://oj.leetcode.com/problems/valid-sudoku/ （三个布尔矩阵）先除3再乘3的方式计算cell

https://oj.leetcode.com/problems/sudoku-solver/ (DFS backtracking)

检测有向图中的环 (DFS + path检测)

http://lintcode.com/en/problem/topological-sorting/ (BFS)

用于查找所有结果模板

public class Solution {    public List<List<Integer>> subsets(int[] S) {        Arrays.sort(S);        List<List<Integer>> result = new ArrayList<List<Integer>>();List<Integer> path = new ArrayList<Integer>();        helper(S, 0, path, result);        return result;    }    private void helper(int[] input, int index, List<Integer> path, List<List<Integer>> result) {        result.add(new ArrayList<Integer>(path));        for (int i = index; i < input.length; i++) {            path.add(input[i]);            helper(input, i + 1, path, result);            path.remove(path.size() - 1);        }    }}

https://leetcode.com/problems/palindrome-partitioning/

https://leetcode.com/problems/restore-ip-addresses/

C12: https://oj.leetcode.com/problems/path-sum-ii/

D5：https://oj.leetcode.com/problems/letter-combinations-of-a-phone-number/ (DFS)

D6：https://oj.leetcode.com/problems/generate-parentheses/ 1子节点: )或( 2生成结果条件:左右括号都是零 3停止条件: 左边剩的多或者左右之一用光

D7：https://oj.leetcode.com/problems/n-queens/ 模板

https://oj.leetcode.com/problems/n-queens-ii/

D9：https://oj.leetcode.com/problems/subsets/ (输入元素不重复)

https://oj.leetcode.com/problems/subsets-ii/ (输入元素重复，结果不允许重复。hashset省事前后比较最好)

D10：https://oj.leetcode.com/problems/combinations/

https://oj.leetcode.com/problems/combination-sum/ （输入元素不重复输入元素可以多次使用）

https://oj.leetcode.com/problems/combination-sum-ii/ （输入元素重复输入元素不可以多次使用）

D11：https://oj.leetcode.com/problems/permutations/ (visited实现)

http://www.lintcode.com/en/problem/permutations/ (swap实现)

https://oj.leetcode.com/problems/permutations-ii/ (hashmap去重省事O(n^n) visited数组去非常重复杂O(n!))

https://oj.leetcode.com/problems/permutation-sequence/ (除(n-1)!, 模(n-1)! 递归)

https://leetcode.com/problems/next-permutation/ (难)

D12：https://oj.leetcode.com/problems/wildcard-matching/ (TODO)

D13：https://oj.leetcode.com/problems/regular-expression-matching/

https://oj.leetcode.com/problems/surrounded-regions/ (非递归BFS/DFS)

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