59.螺旋矩阵II 可以合并并行的多个循环

[ra4-z]

同样用的左闭右开：

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        num = 1
        outer_len = side_len = n
        mat = [[0 for j in range(side_len)] for i in range(side_len)]
        for layer in range((n+1)//2):
            for i in range(side_len-1):
                # This part
                mat[layer][i+layer] = num+i 
                mat[i+layer][outer_len-layer-1] = num+side_len-1+i
                mat[outer_len-layer-1][outer_len-layer-1-i] = num+side_len*2-2+i
                mat[outer_len-layer-1-i][layer] = num+side_len*3-3+i
            if side_len == 1:
                mat[n//2][n//2] = n**2
            num += side_len*4-4
            side_len -= 2
        return mat

作为对比，你们团队的代码：

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        nums = [[0] * n for _ in range(n)]
        startx, starty = 0, 0               # 起始点
        loop, mid = n // 2, n // 2          # 迭代次数、n为奇数时，矩阵的中心点
        count = 1                           # 计数

        for offset in range(1, loop + 1) :      # 每循环一层偏移量加1，偏移量从1开始
            for i in range(starty, n - offset) :    # 从左至右，左闭右开
                nums[startx][i] = count
                count += 1
            for i in range(startx, n - offset) :    # 从上至下
                nums[i][n - offset] = count
                count += 1
            for i in range(n - offset, starty, -1) : # 从右至左
                nums[n - offset][i] = count
                count += 1
            for i in range(n - offset, startx, -1) : # 从下至上
                nums[i][starty] = count
                count += 1                
            startx += 1         # 更新起始点
            starty += 1

        if n % 2 != 0 :			# n为奇数时，填充中心点
            nums[mid][mid] = count 
        return nums

[woaixiuer]

nice

[cholic-1025]

还有更简洁的解法，先定义好前进的方向，“右-下-左-上”，当前进方向上不能继续时（超出数组或者已经被填充），就换到下一个方向继续前进。只需要一个循环和一个if就能完成

 var generateMatrix = function(n) {
    let x = 0, y = 0, current = 1, last = n * n;
    const xDirections = [1, 0, -1, 0]; // 1表示向右，0表示横向不移动，-1表示向左
    const yDirections = [0, 1, 0, -1]; // 1表示向下，0表示纵向不移动，-1表示向上
    let directionIndex = 0;
     
    const result = Array(n);
    for(let i = 0; i < n; i++) {
        result[i] = [];
    }

    while(current <= last) {
        result[y][x] = current;
        const nextX = x + xDirections[directionIndex];
        const nextY = y + yDirections[directionIndex];
        // 超出边界或者下一个位置已经填充过，就换方向
        if (nextX < 0 || nextX >= n || nextY < 0 || nextY >= n || result[nextY][nextX]) {
            directionIndex = (++directionIndex)%4;
        }
        x = x + xDirections[directionIndex];
        y = y + yDirections[directionIndex];
        current++;
    }


    return result;
};