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spiral-matrix-ii.dart (1534B)

      1 //Take a number as the input and return a matrix
      2 //of the same width and height as the number where the 
      3 //values within it are ordered in a spiral formation.
      4 //Ex.
      5 //Input:
      6 // 3
      7 // 1 2 3
      8 // 8 9 4
      9 // 7 6 5
     10 //The time complexity of this code is O(n^2) where n is the input number.
     11 //Time: 260ms Beats: 75%
     12 //Memory: 140.6MB Beats: 75%
     13 
     14 class Solution {
     15   List<List<int>> generateMatrix(int n) {
     16       int placed = 1;
     17       List<List<int>> spiral = [];
     18       int top_margin = 0;
     19       int bottom_margin = n;
     20       int left_margin = 0;
     21       int right_margin = n;
     22       for(int i = 0 ; i < n ; ++i){
     23           spiral.add([]);
     24           for(int x = 0 ; x < n ; ++x){
     25               spiral[spiral.length - 1].add(0);
     26           }
     27       }
     28       while(placed < n*n + 1){
     29           for(int i = left_margin ; i < right_margin; ++i){
     30               spiral[top_margin][i] = placed;
     31               placed += 1;
     32           }
     33           top_margin += 1;
     34 
     35           for(int i = top_margin ; i < bottom_margin ; ++i){
     36               spiral[i][right_margin - 1] = placed;
     37               placed += 1;
     38 
     39           }
     40           right_margin -= 1;
     41           
     42           for(int i = right_margin - 1 ; i >= left_margin ; --i){
     43               spiral[bottom_margin - 1][i] = placed;
     44               placed += 1;
     45 
     46           }
     47           bottom_margin -= 1;
     48 
     49           for(int i = bottom_margin - 1; i >= top_margin ; --i){
     50               spiral[i][left_margin] = placed;
     51               placed += 1;
     52 
     53           }
     54           left_margin += 1;
     55       }
     56 
     57       return spiral;
     58   }
     59 }