[Algorithms(Princeton)] Week1

  1 public class Percolation {
  2     private boolean[] openSites;
  3     private int gridN;
  4     private WeightedQuickUnionUF UF;
  5     private WeightedQuickUnionUF UFfull;
  6 
  7     public Percolation(int N) {
  8         if (N <= 0) {
  9             throw new java.lang.IllegalArgumentException(
 10             "N must be greater than 0");
 11         }
 12         openSites = new boolean[N * N];
 13         gridN = N;
 14         for (int i = 0; i < N * N; ++i) {
 15             openSites[i] = false;
 16         }
 17         // add 2 virtual sites
 18         UF = new WeightedQuickUnionUF(N * N + 2);
 19         UFfull = new WeightedQuickUnionUF(N * N + 1);
 20     }
 21 
 22     private void indexChecker(int i, int j) {
 23         if (i < 1 || j < 1 || i > gridN || j > gridN)
 24             throw new java.lang.IndexOutOfBoundsException();
 25     }
 26 
 27     public void open(int i, int j) {
 28         indexChecker(i, j);
 29 
 30         int indexI = i - 1;
 31         int indexJ = j - 1;
 32 
 33         int osIndex = indexI * gridN + indexJ;
 34         if (openSites[osIndex])
 35             return;
 36         openSites[osIndex] = true;
 37 
 38         int ufIndex = indexI * gridN + indexJ + 1;
 39         if (indexI == 0) {
 40             UF.union(0, ufIndex);
 41             UFfull.union(0, ufIndex);
 42         }
 43         if (indexI == gridN - 1) {
 44             UF.union(ufIndex, gridN * gridN + 1);
 45         }
 46 
 47         boolean bOpen = false;
 48 
 49         // union adjacent open sites
 50         int leftIndexI = indexI;
 51         int leftIndexJ = indexJ - 1;
 52         if (leftIndexJ >= 0) {
 53             bOpen = isOpen(leftIndexI + 1, leftIndexJ + 1);
 54             if (bOpen) {
 55                 int leftUFIndex = leftIndexI * gridN + leftIndexJ + 1;
 56                 UF.union(leftUFIndex, ufIndex);
 57                 UFfull.union(leftUFIndex, ufIndex);
 58             }
 59         }
 60 
 61         int rightIndexI = indexI;
 62         int rightIndexJ = indexJ + 1;
 63         if (rightIndexJ < gridN) {
 64             bOpen = isOpen(rightIndexI + 1, rightIndexJ + 1);
 65             if (bOpen) {
 66                 int rightUFIndex = rightIndexI * gridN + rightIndexJ + 1;
 67                 UF.union(ufIndex, rightUFIndex);
 68                 UFfull.union(ufIndex, rightUFIndex);
 69             }
 70         }
 71 
 72         int upIndexI = indexI - 1;
 73         int upIndexJ = indexJ;
 74         if (upIndexI >= 0) {
 75             bOpen = isOpen(upIndexI + 1, upIndexJ + 1);
 76             if (bOpen) {
 77                 int upUFIndex = upIndexI * gridN + upIndexJ + 1;
 78                 UF.union(upUFIndex, ufIndex);
 79                 UFfull.union(upUFIndex, ufIndex);
 80             }
 81         }
 82 
 83         int downIndexI = indexI + 1;
 84         int downIndexJ = indexJ;
 85         if (downIndexI < gridN) {
 86             bOpen = isOpen(downIndexI + 1, downIndexJ + 1);
 87             if (bOpen) {
 88                 int downUFIndex = downIndexI * gridN + downIndexJ + 1;
 89                 UF.union(ufIndex, downUFIndex);
 90                 UFfull.union(ufIndex, downUFIndex);
 91             }
 92         }
 93     }
 94 
 95     public boolean isOpen(int i, int j) {
 96         indexChecker(i, j);
 97         return (openSites[(i - 1) * gridN + j - 1]);
 98     }
 99 
100     public boolean isFull(int i, int j) {
101         indexChecker(i, j);
102         int indexI = i - 1;
103         int indexJ = j - 1;
104 
105         int osIndex = indexI * gridN + indexJ;
106         int ufIndex = osIndex + 1;
107 
108         boolean bOpen = isOpen(i, j);
109         boolean isFull = UFfull.connected(0, ufIndex);
110         return (bOpen && isFull);
111     }
112 
113     public boolean percolates() {
114         if (gridN == 1)
115             return (openSites[0]);
116         return UF.connected(0, gridN * gridN + 1);
117     }
118 }
You can see Percolation problem here.
http://coursera.cs.princeton.edu/algs4/assignments/percolation.html
This problem is something related to Union-Find.