[LeetCode100]Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,
Given the following matrix:

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

You should return [1,2,3,6,9,8,7,4,5].

Analysis:

We could solve this problem straight forward. Output is element in order: up->right->down->left layer from layer. 

every time we ouput its most outside rectangle, use (x1,y1) (x2,y2) represent

it can be achieved in while loop, the codition is x1<=x2 && y1<=y2

Java

public List<Integer> spiralOrder(int[][] matrix) {
        ArrayList<Integer> result = new ArrayList<Integer>();
    int x1 = 0;
    int y1 = 0;
    int x2 = matrix.length-1;
    if(x2<0) return result;
    int y2 = matrix[0].length-1;
    while(x1<=x2 && y1<=y2){
    	for(int i=y1;i<=y2;i++){//right
    		result.add(matrix[x1][i]);
    	}
    	for(int j=x1+1;j<=x2;j++){//down
    		result.add(matrix[j][y2]);
    	}
    	if(x1!=x2){
    		for(int i=y2-1;i>=y1;i--){//left
    			result.add(matrix[x2][i]);
    		}
    	}
    	if(y1!=y2){//up
    		for(int j=x2-1;j>x1;j--){
    			result.add(matrix[j][y1]);
    		}
    	}
    	x1++; y1++; x2--;y2--;
    }
    return result;
    }

c++

vector<int> spiralOrder(vector<vector<int> > &matrix) {
    vector<int> result;
     if(matrix.size() == 0) return result;
     int x1 = 0;
     int y1 = 0;
     int x2 = matrix.size() - 1;
     int y2 = matrix[0].size() - 1;
     while(x1<=x2 && y1<=y2){
        //up row
        for(int j = y1; j<=y2; ++j){
            result.push_back(matrix[x1][j]);
        }
        // right column
        for(int i = x1+1; i<=x2; ++i){
            result.push_back(matrix[i][y2]);
        }
        
        if(x2 !=x1){
        // bottom row
        for(int j = y2-1; j>=y1; --j){
            result.push_back(matrix[x2][j]);
        }}
       
        if(y2 != y1){
        // left column
        for(int i = x2-1; i>x1; --i){
            result.push_back(matrix[i][y1]);
        }}
        x1++, y1++, x2--, y2--;
     }
     return result;
    }