Spiral and Zigzag

【LeetCode】

虽然感觉spiral matrix 两道题和 zigzag conversion 那道题没有太多联系，但是，毕竟都是相当于数学上的找规律题目。

这种优雅的题目就应该用下面这种优雅的代码写法。

054 Spiral Matrix

 /* Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

 For example,
 Given the following matrix:

 [
  [ 1, 2, 3 ],
  [ 4, 5, 6 ],
  [ 7, 8, 9 ]
 ]
 You should return [1,2,3,6,9,8,7,4,5].
  */

 class Solution {
     public List<Integer> spiralOrder(int[][] matrix) {
         List<Integer> res = new ArrayList<>();
         if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return res;
         int beginX = 0, endX = matrix[0].length - 1;
         int beginY = 0, endY = matrix.length - 1;
         while(true){
             //from left to right
             for(int i = beginX; i <= endX; i++) res.add(matrix[beginY][i]);
             if(++beginY > endY) break;
             //from top to bottom
             for(int i = beginY; i <= endY; i++) res.add(matrix[i][endX]);
             if(beginX > --endX) break;
             //from right to left
             for(int i = endX; i >= beginX; i--) res.add(matrix[endY][i]);
             if(beginY > --endY) break;
             //from bottom to top
             for(int i = endY; i >= beginY; i--) res.add(matrix[i][beginX]);
             if(++beginX > endX) break;
         }
         return res;
     }
 }

059 Spiral Matrix II

 /* Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

 For example,
 Given n = 3,

 You should return the following matrix:
 [
  [ 1, 2, 3 ],
  [ 8, 9, 4 ],
  [ 7, 6, 5 ]
 ] */

 class Solution {
     public int[][] generateMatrix(int n) {
         int[][] res = new int[n][n];
         int beginX = 0, endX = n - 1;
         int beginY = 0, endY = n - 1;
         int flag = 1;
         while(true){
             for(int i = beginX; i <= endX; i++) res[beginY][i] = flag++;
             if(++beginY > endY) break;
             for(int i = beginY; i <= endY; i++) res[i][endX] = flag++;
             if(beginX > --endX) break;
             for(int i = endX; i >= beginX; i--) res[endY][i] = flag++;
             if(beginY > --endY) break;
             for(int i = endY; i >= beginY; i--) res[i][beginX] = flag++;
             if(++beginX > endX) break;
         }
         return res;
     }
 }

006 Zigzag Conversion

 /* The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

 P   A   H   N
 A P L S I I G
 Y   I   R
 And then read line by line: "PAHNAPLSIIGYIR"
 Write the code that will take a string and make this conversion given a number of rows:

 string convert(string text, int nRows);
 convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".
  */

 class Solution {
 public:
     string convert(string s, int numRows) {
         if(numRows <=  || s.length() < numRows)
             return s;
         string res;
         for(int i = ;i < numRows;++i)
         {
             for(int j = i;j < s.length();j +=  * (numRows - ))
             {
                 res += s[j];
                 if(i >  && i < numRows - )
                 {
                     if(j +  * (numRows -  - i) < s.length())
                         res += s[j +  * (numRows -  - i)];
                 }
             }
         }
         return res;
     }
 };