solve: pacific atlantic water flow

Author: wogha95

pacific-atlantic-water-flow/wogha95.js

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+/**
+ * pacific(0행, 0열), atlantic(row-1행, column-1열)에서 높이가 같거나 높은 곳으로 순회한다.
+ * 그리고 pacific에서 온 물과 atlantic에서 온 물이 만나는 곳을 정답으로 만든다.
+ *
+ * TC: O(row * column)
+ * queue에 최대 row * column만큼 들어갑니다.
+ *
+ * SC: O(row * column)
+ * pacific 또는 atlantic에 최대 row * column만큼 들어갑니다.
+ */
+
+/**
+ * @param {number[][]} heights
+ * @return {number[][]}
+ */
+var pacificAtlantic = function (heights) {
+  const ROW = heights.length;
+  const COLUMN = heights[0].length;
+  const DIRECTION = [
+    [-1, 0],
+    [1, 0],
+    [0, -1],
+    [0, 1],
+  ];
+  const result = [];
+  const queue = [];
+
+  for (let c = 0; c < COLUMN; c++) {
+    queue.push([0, c]);
+  }
+  for (let r = 1; r < ROW; r++) {
+    queue.push([r, 0]);
+  }
+
+  const pacific = new Set();
+  while (queue.length > 0) {
+    const [row, column] = queue.shift();
+    pacific.add(generateKey(row, column));
+    for (const [directionR, directionC] of DIRECTION) {
+      const [nextRow, nextColumn] = [row + directionR, column + directionC];
+      if (
+        isValidPosition(nextRow, nextColumn) &&
+        heights[row][column] <= heights[nextRow][nextColumn] &&
+        !pacific.has(generateKey(nextRow, nextColumn))
+      ) {
+        queue.push([nextRow, nextColumn]);
+      }
+    }
+  }
+
+  for (let c = 0; c < COLUMN; c++) {
+    queue.push([ROW - 1, c]);
+  }
+  for (let r = 0; r < ROW - 1; r++) {
+    queue.push([r, COLUMN - 1]);
+  }
+
+  const atlantic = new Set();
+  while (queue.length > 0) {
+    const [row, column] = queue.shift();
+    const key = generateKey(row, column);
+    atlantic.add(key);
+    if (pacific.has(key)) {
+      pacific.delete(key);
+      result.push([row, column]);
+    }
+    for (const [directionR, directionC] of DIRECTION) {
+      const [nextRow, nextColumn] = [row + directionR, column + directionC];
+      if (
+        isValidPosition(nextRow, nextColumn) &&
+        heights[row][column] <= heights[nextRow][nextColumn] &&
+        !atlantic.has(generateKey(nextRow, nextColumn))
+      ) {
+        queue.push([nextRow, nextColumn]);
+      }
+    }
+  }
+
+  return result;
+
+  function isValidPosition(row, column) {
+    if (row < 0 || ROW <= row) {
+      return false;
+    }
+    if (column < 0 || COLUMN <= column) {
+      return false;
+    }
+    return true;
+  }
+
+  function generateKey(row, column) {
+    return `${row},${column}`;
+  }
+};