LeetCode Notes: Spiral Matrix

#leetcode

Question

Given an m x n matrix, return all elements of the matrix in spiral order.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]

Output: [1,2,3,6,9,8,7,4,5]

Example 2:

Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]

Output: [1,2,3,4,8,12,11,10,9,5,6,7]

Constraints:

  • m == matrix.length
  • n == matrix[i].length
  • 1 <= m, n <= 10
  • -100 <= matrix[i][j] <= 100

Solution

Analysis:

  1. Set up/ down/ left/ right start and end position variables
  2. Traverse horizontally and vertically according to the requirements, each time one direction is traversed, the start and end positions will be reduced to achieve the spiral effect

Code:

/**
 * @param {number[][]} matrix
 * @return {number[]}
 */
var spiralOrder = function(matrix) {
    // is empty judgment
    if(matrix.length === 0) return []

    // Store the result array
    const result = []

    // Get the initial element position information
    let left = 0, right = matrix[0].length-1,
        top = 0, bottom = matrix.length-1

    while(true){
        // Traverse to the right
        for(let i = left; i <= right; i++){
            result.push(matrix[top][i])
        }
        // The traversal is over, the top value just traversed is no longer used, the upper boundary needs to move down by +1, if the top value exceeds the bottom value, it means that the vertical traversal has ended, exit the loop
        if(++top> bottom) break

        // traverse down
        for(let i = top; i <= bottom; i++){
            result.push(matrix[i][right])
        }
        // The traversal is over, the right value just traversed is no longer used, the right boundary needs to be moved to the left by -1, if the right value is less than the left value, it means that the horizontal traversal has ended, exit the loop
        if(--right <left) break

        // Traverse left
        for(let i = right; i >= left; i--){
            result.push(matrix[bottom][i])
        }
        // The traversal is over, the bottom value just traversed is no longer used, the lower boundary needs to move up by -1, if the bottom value is less than the top value, it means that the vertical traversal has ended, exit the loop
        if(--bottom <top) break

        // traverse upward
        for(let i = bottom; i >= top; i--){
            result.push(matrix[i][left])
        }
        // The traversal is over, the left value just traversed is no longer used, the left boundary needs to move to the right by +1, if the left value is greater than the right value, it means that the horizontal traversal has ended, exit the loop
        if(++left> right) break

    }

    return result
    
};

Reference

Comments