leetcode-spiral-matrix-i-ii

Verbatim https://www.dazhuanlan.com/2019/08/26/5d62fafb4de84/

Subject to the effect

　　https://leetcode.com/problems/spiral-matrix/

　　https://leetcode.com/problems/spiral-matrix-ii/

　　These two questions is essentially a question, are generates print matrix or spiral

Topic analysis

　　I was beginning to realize each row or each column a few prints, leaving the next column or the next line treatment, this has led finally, a special judge in the end is the remaining 1 row / column, or two rows / columns. The code does not result in an extremely elegant, although AC. I think the goal is not just brush leetcode AC, but also to the pursuit of time / space complexity, and elegant code. Read overwhelmingly answer disscuss area, each is a simple "cut" rows or columns can be very elegant solution out. As Spiral Matrix II but more simply, the subject of the request is to generate a square spiral, it is possible to almost completely code reuse.

Code

　　Spiral Matrix:

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public class { public List<Integer> spiralOrder(int[][] matrix) { List<Integer> ans = new ArrayList<Integer>(); if (matrix == null || matrix.length == 0 || matrix[ 0].length == 0) { return years; } int m = matrix.length; int n = matrix[ 0].length; int up = 0; int down = m - 1; int left = 0; int right = n - 1; while ( true) { for ( int col = left; col <= right; col++) { ans.add(matrix[up][col]); } up++; if (up > down) { break; } for ( int row = up; row <= down; row++) { ans.add(matrix[row][right]); } right--; if (right < left) { break; } for ( int col = right; col >= left; col--) { ans.add(matrix[down][col]); } down--; if (down < up) { break; } for ( int row = down; row >= up; row--) { ans.add(matrix[row][left]); } left++; if (left > right) { break; } } return ans; } }

　　Spiral Matrix II:

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public class Solution { public int[][] generateMatrix( int n) { int[][] matrix = new int[n][n]; int up = 0; int down = n - 1; int left = 0; int right = n - 1; int c = 0; while ( true) { for ( int col = left; col <= right; col++) { matrix[up][col] = ++c; } up++; if (up > down) { break; } for ( int row = up; row <= down; row++) { matrix[row][right] = ++c; } right--; if (right < left) { break; } for ( int col = right; col >= left; col--) { matrix[down][col] = ++c; } down--; if (down < up) { break; } for ( int row = down; row >= up; row--) { matrix[row][left] = ++c; } left++; if (left > right) { break; } } return matrix; } }