leetcode59.Spiral Matrix II

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题目要求

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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 ]
]

也就是将递加的数字按照顺时针的顺序依次填入数组之中

这道题目联系到Spiral Matrix I，其实就相当好解决了。Spiral Matrix I可以参考我的这篇博客

具体代码

在参考完这篇博客后，就会发现，这里其实就是将读取数据反过来改为填入数据，代码如下：

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public int[][] generateMatrix(int n) {
    int[][] result = new int[n][n];
    int rowStart = 0;
    int rowEnd = n-1;
    int colStart = 0;
    int colEnd = n-1;
    
    int number = 1;
    while(rowStart<=rowEnd && colStart<=colEnd){
        for(int i = colStart ; i<=colEnd ; i++){
            result[rowStart][i] = number;
            number++;
        }
        
        rowStart++;
        
        for(int i = rowStart ; i<=rowEnd ; i++){
            result[i][colEnd] = number;
            number++;
        }
        colEnd--;
        
        if(rowStart <= rowEnd){
            for(int i = colEnd ; i>=colStart ; i--){
                result[rowEnd][i] = number;
                number++;
            }
        }
        rowEnd--;
        
        if(colStart<= colEnd){
            for(int i = rowEnd ; i>= rowStart ; i--){
                result[i][colStart] = number;
                number++;
            }
        }
        colStart++;
    }
    return result;
}