public int TrapWater2(int[,] heights) {
if(heights == null || heights.GetLength(0) == 0 || heights.GetLength(1) == 0) return 0;
var pq = new PriorityQueue<Cell>((a,b) -> Integer.Compare(a.ht,b.ht));
int m = heights.GetLength(0);
int n = heights.GetLength(1);
bool[,] visited = new bool[m,n];
// 1. Add all border cells into pq
for(int i = 0; i < m; i++) {
visited[i,0] = true;
visited[i,n-1] = true;
pq.offer(new Cell(i,0,heights[i,0]);
pq.offer(new Cell(i,n-1,heights[i,n-1]);
}
for(int i = 0; i < n; i++) {
visited[0,i] = true;
visited[m-1,i] = true;
pq.offer(new Cell(i,0,heights[0,i]);
pq.offer(new Cell(i,n-1,heights[m-1,i]);
}
int max = Int32.MinValue, sum = 0;
// 2. Pick smallest cell, visit neighbors
int[,] dirs = new int[,] {{-1,0}, {1,0}, {0,1}, {0,-1}};
while(pq.Count != 0) {
Cell curr = pq.poll();
max = Math.Max(curr.ht, max);
if(curr.ht < max) {
sum += max - curr.ht;
}
for(int[] dir in dirs) {
int row = cell.row + dir[0];
int col = cell.col + dir[1];
if(row >= 0 && row < m && col >= 0 && col < n && !visited[row,col]) {
visited[row,col] = true;
pq.offer(new Cell(row, col, heights[row,col]));
}
}
}
return sum;
}
/// <summary>
///
/// </summary>
/// <param name="a"></param>
/// <param name="b"></param>
/// <returns>a < b: - 1; a == b: 0; a > b: == 1</b></returns>
public static int Compare(Rational a, Rational b)
{
Natural lcm = Natural.LCM(a.Denominator, b.Denominator);
return(Integer.Compare(a.Numerator * lcm / a.Denominator, b.Numerator * lcm / a.Denominator));
}
private static int Compare(int x, int y)
{
return(Integer.Compare(x, y));
}