二维数组的花式遍历技巧

二维数组的花式遍历技巧

旋转图像

https://leetcode-cn.com/problems/rotate-image/

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func rotate(matrix [][]int)  {
    n := len(matrix)
    // 对角线反转矩阵
    for i := 0; i < n; i++ {
        for j := i + 1; j < n; j++ {
            matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
        }
    }
    // 反转每一行
    for i := 0; i < n; i++ {
        reverse(matrix[i])
    }
}

func reverse(list []int) {
    i, j := 0, len(list) - 1
    for i < j {
        list[i], list[j] = list[j], list[i]
        i++
        j--
    }
}

螺旋矩阵

https://leetcode-cn.com/problems/spiral-matrix/

定义好这几个 bound，然后在它们的范围内螺旋遍历即可。

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func spiralOrder(matrix [][]int) []int {
    m, n := len(matrix), len(matrix[0])
    upperBound, rightBound, lowerBound, leftBound := 0, n-1, m-1, 0
    result := make([]int, m * n)
    count := 0
    for count < m * n {
        if upperBound <= lowerBound {
            for i := leftBound; i <= rightBound; i++ {
                result[count] = matrix[upperBound][i]
                count++
            }
            upperBound++
        }
        if rightBound >= leftBound {
            for i := upperBound; i <= lowerBound; i++ {
                result[count] = matrix[i][rightBound]
                count++
            }
            rightBound--
        }
        if lowerBound >= upperBound {
            for i := rightBound; i >= leftBound; i-- {
                result[count] = matrix[lowerBound][i]
                count++
            }
            lowerBound--
        }
        if leftBound <= rightBound {
            for i := lowerBound; i >= upperBound; i-- {
                result[count] = matrix[i][leftBound]
                count++
            }
            leftBound++
        }
    }
    return result
}

螺旋矩阵 II

就是刚刚那道题的反过程。

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func generateMatrix(n int) [][]int {
    matrix := make([][]int, n)
    for i := range matrix {
        matrix[i] = make([]int, n)
    }

    upperBound, rightBound, lowerBound, leftBound := 0, n-1, n-1, 0
    count := 1
    for count <= n * n {
        if upperBound <= lowerBound {
            for i := leftBound; i <= rightBound; i++ {
                matrix[upperBound][i] = count
                count++
            }
            upperBound++
        }
        if rightBound >= leftBound {
            for i := upperBound; i <= lowerBound; i++ {
                matrix[i][rightBound] = count
                count++
            }
            rightBound--
        }
        if lowerBound >= upperBound {
            for i := rightBound; i >= leftBound; i-- {
                matrix[lowerBound][i] = count
                count++
            }
            lowerBound--
        }
        if leftBound <= rightBound {
            for i := lowerBound; i >= upperBound; i-- {
                matrix[i][leftBound] = count
                count++
            }
            leftBound++
        }
    }
    return matrix
}