Assignment 4

deliaioanac/assignment4/Islands.cpp

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+#include <vector>
+#include <iostream>
+
+// Function that return the 'head' of the island patch i belongs to
+int find(int i, std::vector<int> &parent) {
+    int head = i, aux;
+
+    while (head != parent[head]) {
+        head = parent[head];
+    }
+
+    // Path compression (make the parent of every node along
+    // the way to be the head of the whole island)
+    while (i != parent[i]) {
+        aux = parent[i];
+        parent[i] = head;
+        i = aux;
+    }
+
+    return head;
+}
+
+// Unite two islands
+void unite(int i, int j, std::vector<int> &parent, std::vector<int> &rank) {
+    if (rank[i] > rank[j]) {
+        parent[j] = i;
+    } else {
+        parent[i] = j;
+    }
+
+    if (rank[i] == rank[j]){
+        rank[j] ++;
+    }
+}
+
+int countingIslands(const std::vector<std::vector<bool> > &map) {
+    // If there is no map, there can be no islands
+    if (map.empty()) {
+        std::cout << "The map is empty!" << std::endl;
+        return 0;
+    }
+
+    // The initial number of distinct possible patches of land
+    int numberOfIslands = map.size() * map[0].size();
+    std::vector<int> parent(numberOfIslands), rank(numberOfIslands);
+
+    for (int i = 0; i < map.size(); i ++) {
+        for (int j = 0; j < map[i].size(); j ++) {
+            if (map[i][j]) {
+                parent[i * map.size() + j] = i * map.size() + j;
+                rank[i * map.size() + j] = 0;
+
+                // Check if these is a patch of land above this one and,
+                // if there is, unite its island to this patch of land
+                if (i > 0 && map[i - 1][j]) {
+                    unite(find(i * map.size() + j, parent),
+                          find((i - 1) * map.size() + j, parent), parent, rank);
+                    numberOfIslands --;
+                }
+
+                // Check if there is a patch of land to the left of this
+                // one and, if there is and it does not belong to the
+                // same island as a patch of land above, unite their islands
+                if (j > 0 && map[i][j - 1] &&
+                    (i == 0 || !map[i - 1][j] ||
+                    find((i - 1) * map.size() + j, parent) !=
+                    find(i * map.size() + (j - 1), parent))) {
+                    unite(find(i * map.size() + j, parent),
+                          find(i * map.size() + (j - 1), parent), parent, rank);
+                    numberOfIslands --;
+                }
+            } else {
+                // If it is not land, it cannot be an island
+                numberOfIslands --;
+            }
+        }
+    }
+
+    return numberOfIslands;
+}

deliaioanac/assignment4/IslandsUnitTests.cpp

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+#include "Islands.cpp"
+#include <gtest/gtest.h>
+
+std::vector<std::vector<bool> > map;
+
+TEST(CountingIslandsTest, EmptyMap) {
+    EXPECT_EQ(0, countingIslands(map));
+}
+
+TEST(CountingIslandsTest, ExampleMap1) {
+    map = {{false, true, false, true},
+           {true, true, false, false},
+           {false, false, true, false},
+           {false, false, true, false}};
+
+    EXPECT_EQ(3, countingIslands(map));
+}
+
+TEST(CountingIslandsTest, ExampleMap2) {
+    map = {{false, true, false, true},
+           {true, true, true, false},
+           {false, false, true, false},
+           {true, false, true, false}};
+
+    EXPECT_EQ(3, countingIslands(map));
+}
+
+TEST(CountingIslandsTest, ExampleMap3) {
+    map = {{true, true, false, true},
+           {false, false, false, false},
+           {false, false, false, false},
+           {true, false, false, true}};
+
+    EXPECT_EQ(4, countingIslands(map));
+}
+
+TEST(CountingIslandsTest, NoIslands) {
+    map = {{false, false, false, false},
+           {false, false, false, false},
+           {false, false, false, false},
+           {false, false, false, false}};
+
+    EXPECT_EQ(0, countingIslands(map));
+}
+
+TEST(CountingIslandsTest, NoWaterFullIsland) {
+    map = {{true, true},
+           {true, true}};
+
+    EXPECT_EQ(1, countingIslands(map));
+}
+
+int main(int argc, char **argv) {
+    testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}