LC 756. Pyramid Transition Matrix

We are stacking blocks to form a pyramid. Each block has a color which is a one letter string, like `'Z'`.

For every block of color `C` we place not in the bottom row, we are placing it on top of a left block of color `A` and right block of color `B`. We are allowed to place the block there only if `(A, B, C)` is an allowed triple.

We start with a bottom row of bottom, represented as a single string. We also start with a list of allowed triples allowed. Each allowed triple is represented as a string of length 3.

Return true if we can build the pyramid all the way to the top, otherwise false.

Example 1:

Input: bottom = "XYZ", allowed = ["XYD", "YZE", "DEA", "FFF"]

Output: true

Explanation:

We can stack the pyramid like this:

    A

   / \

  D   E

 / \ / \

X   Y   Z

This works because ('X', 'Y', 'D'), ('Y', 'Z', 'E'), and ('D', 'E', 'A') are allowed triples.

Example 2:

Input: bottom = "XXYX", allowed = ["XXX", "XXY", "XYX", "XYY", "YXZ"]

Output: false

Explanation:

We can't stack the pyramid to the top.

Note that there could be allowed triples (A, B, C) and (A, B, D) with C != D.

Note:

bottom will be a string with length in range [2, 8].
allowed will have length in range [0, 200].
Letters in all strings will be chosen from the set {'A', 'B', 'C', 'D', 'E', 'F', 'G'}.

map + backtracing

Runtime: 9 ms, faster than 80.22% of Java online submissions for Pyramid Transition Matrix.

class Solution {

  private Map<String, List<Character>> mp = new HashMap<>();

  public boolean pyramidTransition(String bottom, List<String> allowed) {

    for(int i=; i<allowed.size(); i++){

      String tmp = allowed.get(i).substring(,);

      if(mp.containsKey(tmp)){

        mp.get(tmp).add(allowed.get(i).charAt(allowed.get(i).length()-));

      }else{

        mp.put(tmp, new ArrayList<>());

        mp.get(tmp).add(allowed.get(i).charAt(allowed.get(i).length()-));

      }

    }

//    for(String s : mp.keySet()){

//      System.out.print(s + " " + mp.get(s) + "\n");

//    }

    return helper(bottom, "", );

  }

  public boolean helper(String bottom, String up, int index){

    if(bottom.length() == ){

      return true;

    }else {

      String tmp = bottom.substring(index, index+);

      if(!mp.containsKey(tmp)) return false;

      List<Character> clist = mp.get(tmp);

      if(index+ == bottom.length()){

        for(char x : clist){

          String finalup = up + String.valueOf(x);

          if(helper(finalup, "", )) return true;

        }

      }else {

        for(char x : clist){

          if(helper(bottom, up+String.valueOf(x), index+)) return true;

        }

      }

    }

    return false;

  }

}

巴特西

LC 756. Pyramid Transition Matrix

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