PIPOTW: Outward Counterclockwise Spiral Matrix Traversal

gistfile1.m

- (NSArray*)spirralArrayFromGridOfWidth:(int)width height:(int)height startline:(int)line column:(int)column{
    NSMutableArray *returnArray = [NSMutableArray new];
    int currentDirectionIndex = 0;
    int currentInt;
    int nextPivotal = 3;
    int numOfPivotal = 1;
    line++;
    
    for(int i=1;i<=width*height; i++){
        if(nextPivotal == i){
            numOfPivotal++;
            nextPivotal += ceil((float)numOfPivotal/2);
            currentDirectionIndex++;
        }
        
        switch (currentDirectionIndex%4) {
            case 0:
                // Up
                line--;
                break;
                
            case 1:
                // Left
                column--;
                break;
                
            case 2:
                // Down
                line++;
                break;
                
            case 3:
                // Right
                column++;
                break;
        }
        
        currentInt = (line-1)*width+column;
        if(currentInt<=0||line>height||column>width||!column||!line){
            i--;
        } else {
            [returnArray addObject:[NSNumber numberWithInt:currentInt]];
        }
    }
    return returnArray;
}