week9 mission - Pacific Atlantic Water Flow

Author: dev-jonghoonpark

pacific-atlantic-water-flow/dev-jonghoonpark.md

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+- 문제: https://leetcode.com/problems/pacific-atlantic-water-flow/
+- 풀이: https://algorithm.jonghoonpark.com/2024/03/03/leetcode-417
+
+```java
+public class Solution {
+	public List<List<Integer>> pacificAtlantic(int[][] heights) {
+		List<List<Integer>> result = new ArrayList<>();
+
+		for (int i = 0; i < heights.length; i++) {
+			for (int j = 0; j < heights[0].length; j++) {
+				System.out.printf("\n\ninit Flow : %d, %d\n", i, j);
+				Flow flow = new Flow();
+				dfs(flow, heights, Integer.MAX_VALUE, i, j);
+				if (flow.flowToAtlanticOcean && flow.flowToPacificOcean) {
+					result.add(List.of(i, j));
+				}
+			}
+		}
+
+		return result;
+	}
+
+	private void dfs(Flow flow, int[][] heights, int prev, int i, int j) {
+		if (i == -1 || j == -1) {
+			flow.flowToPacificOcean = true;
+			return;
+		}
+
+		if (i == heights.length || j == heights[0].length) {
+			flow.flowToAtlanticOcean = true;
+			return;
+		}
+
+		if (heights[i][j] == -1 || heights[i][j] > prev || flow.flowToAtlanticOcean && flow.flowToPacificOcean) {
+			return;
+		}
+
+		int currentHeight = heights[i][j];
+		heights[i][j] = -1;
+
+		dfs(flow, heights, currentHeight, i + 1, j);
+		dfs(flow, heights, currentHeight, i - 1, j);
+		dfs(flow, heights, currentHeight, i, j + 1);
+		dfs(flow, heights, currentHeight, i, j - 1);
+
+		heights[i][j] = currentHeight;
+	}
+}
+
+class Flow {
+	boolean flowToPacificOcean;
+	boolean flowToAtlanticOcean;
+}
+```
+
+## TC, SC
+
+heights의 길이를 `w`, heights[0]의 길이를 `h`로 정의했을 때,
+이 코드의 시간 복잡도는 `O((w \* h)^2)`, 공간 복잡도는 `O(w \* h)` 이다.
+시간 복잡도가 저렇게 나온 이유는 모든 좌표에 대해서 dfs를 진행하기 때문이다.