Leetcode Permutation

原创于 2019-06-07 23:36:09 发布 · 264 阅读

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本文深入探讨了如何使用深度优先搜索(DFS)算法解决字符串全排列问题，通过树形结构展示递归过程，详细解释了从输入字符串到输出所有可能组合的实现细节。

Problem

Give a string, like “abc”, return all the possible combinations (all the chars are different)

example:
input: “abc”
output: [abc, acb, bac, bca, cab, cba]

Analysis

obviously, this problem can be solved by dfs. We should know that all the dfs problem can be shown as a tree form. So once we transfer the problem into a tree, the problem is solved.

             " "
      /       |      \
   a          b        c
   | \        | \      | \
  ab  ac      ba bc    ca cb
  |   |       |  |     |   |
 abc acb    bac bca   cab cba

Coding

// An highlighted block
class Solution1 {
	public static List<String> mutation(String str){
		
		List<String> res = new LinkedList<String>();
		
		String temp = "";
		dfs(str, res, temp, str.length());
		
		
		return res;
	}
	
	public static void dfs(String str, List<String> res, String temp, int len ) {
		
		// base case
		if (temp.length() == len) {
			res.add(temp);
			return;
		}
		
		// recursive rule
		for (int i=0; i<str.length(); i++) {
			if (temp.indexOf(str.charAt(i)) < 0) {
				dfs(str, res, temp + str.charAt(i), str.length());
			}		
		}		
	}