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.
