LeetCode-Spiral Matrix II

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受上一题启发知道要keep四个变量分别为四个角的边界一层一层填充

public class Solution {    public int[][] generateMatrix(int n) {        int [][] res = new int [n][n];        int i = 1;        int colStart = 0;        int colEnd = n - 1;        int rowStart = 0;        int rowEnd = n - 1;        while ( i <= n * n ) {            //go right            for ( int j = colStart; j <= colEnd; j ++ ){                res[rowStart][j] = i;                i ++;            }            rowStart ++;            //go down            for ( int j = rowStart; j <= rowEnd; j ++ ){                res[j][colEnd] = i;                i ++;            }            colEnd --;            // go left;            for ( int j = colEnd; j >= colStart; j -- ){                res[rowEnd][j] = i;                i ++;            }            rowEnd --;            // go up            for ( int j = rowEnd; j >= rowStart; j -- ){                res[j][colStart] = i;                i ++;            }            colStart ++;        }        return res;    }}

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