Implement Pacific Atlantic Water Flow algorithm

Author: harshithasudhakar

Graphs/Problems/PacificAtlanticWaterFlow.java

@@ -0,0 +1,71 @@
+class PacificAtlanticWaterFlow {
+    public List<List<Integer>> pacificAtlantic(int[][] heights) {
+        int n = heights.length;
+        int m = heights[0].length;
+
+        boolean[][] canReachPacific = new boolean[n][m];
+        boolean[][] canReachAtlantic = new boolean[n][m];
+
+        List<List<Integer>> result = new ArrayList<>();
+
+        for(int i = 0; i<n; i++){
+            for(int j = 0; j<m; j++){
+                if(i == 0){
+                    dfs(i, j, m, n, canReachPacific, heights);
+                }
+                if(j == 0){
+                    dfs(i, j, m, n, canReachPacific, heights);
+                }
+                if(i == n-1){
+                    dfs(i, j, m, n, canReachAtlantic, heights);
+                }
+                if(j == m-1){
+                    dfs(i, j, m, n, canReachAtlantic, heights);
+                }
+            }
+        }
+
+        for(int i = 0; i<n; i++){
+            for(int j = 0; j<m; j++){
+                if(canReachPacific[i][j] == true && canReachAtlantic[i][j] == true){
+                    List<Integer> coordinates = new ArrayList<>();
+                    coordinates.add(i);
+                    coordinates.add(j);
+                    result.add(coordinates);
+                }
+            }
+        }
+
+        return result;
+
+    }
+
+    static void dfs(int i, int j, int m, int n, boolean[][] visited, int[][] heights){
+        if(i<0 || j<0 || i>=n || j>=m){
+            return;
+        }
+
+        if(visited[i][j] == true){
+            return;
+        }
+
+        visited[i][j] = true;
+
+        // up
+        if (i - 1 >= 0 && heights[i - 1][j] >= heights[i][j]) {
+            dfs(i - 1, j, m, n, visited, heights);
+        }
+        // down
+        if (i + 1 < n && heights[i + 1][j] >= heights[i][j]) {
+            dfs(i + 1, j, m, n, visited, heights);
+        }
+        // left
+        if (j - 1 >= 0 && heights[i][j - 1] >= heights[i][j]) {
+            dfs(i, j - 1, m, n, visited, heights);
+        }
+        // right
+        if (j + 1 < m && heights[i][j + 1] >= heights[i][j]) {
+            dfs(i, j + 1, m, n, visited, heights);
+        }
+    }
+}