Spiral Matrix

Medium

Python

def spiral_order(matrix):
    res=[]
    while matrix:
        res+=matrix.pop(0)
        matrix=list(zip(*matrix))[::-1]
    return res

Java

public List<Integer> spiralOrder(int[][] m){
    List<Integer> res=new ArrayList<>();
    while(m.length>0&&m[0].length>0){
        for(int x:m[0]) res.add(x);
        int[][] t=new int[m[0].length][m.length-1];
        for(int r=1;r<m.length;r++) for(int c=m[r].length-1;c>=0;c--) t[c][r-1]=m[r][c];
        m=t;
    } return res;
}

Key Insight

zip(*matrix) is Python's most powerful matrix trick.

Python → Java Differences

zip(*matrix) Python transpose trick
[::-1] rotation vs loops
Java needs explicit transposition

Python

def spiral_order(matrix):
    res=[]
    while matrix:
        res+=matrix.pop(0)
        matrix=list(zip(*matrix))[::-1]
    return res

Java

public List<Integer> spiralOrder(int[][] m){
    List<Integer> res=new ArrayList<>();
    while(m.length>0&&m[0].length>0){
        for(int x:m[0]) res.add(x);
        int[][] t=new int[m[0].length][m.length-1];
        for(int r=1;r<m.length;r++) for(int c=m[r].length-1;c>=0;c--) t[c][r-1]=m[r][c];
        m=t;
    } return res;
}

Algorithm Steps

1. Take top row
2. Rotate 90 degrees
3. Repeat

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