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 <= 1 || s.length() < numRows) 
            return s;
        string res;
        for(int i = 0;i < numRows;++i)
        {
            for(int j = i;j < s.length();j += 2 * (numRows - 1))
            {
                res += s[j];
                if(i > 0 && i < numRows - 1)
                {
                    if(j + 2 * (numRows - 1 - i) < s.length())
                        res += s[j + 2 * (numRows - 1 - i)];
                }
            }
        }
        return res;
    }
};