0417-pacific-atlantic-water-flow.js

/**
 * Pacific Atlantic Water Flow
 * Time Complexity: O(rows * columns)
 * Space Complexity: O(rows * columns)
*/
var pacificAtlantic = function (heights) {
    const totalRows = heights.length;
    const totalColumns = heights[0].length;
    const waterFlowResult = [];

    const pacificReachableCells = Array.from({ length: totalRows }, () => Array(totalColumns).fill(false));
    const atlanticReachableCells = Array.from({ length: totalRows }, () => Array(totalColumns).fill(false));

    function exploreOceanFlow(currentRow, currentColumn, gridHeights, oceanPathGrid) {
        if (oceanPathGrid[currentRow][currentColumn]) {
            return;
        }
        oceanPathGrid[currentRow][currentColumn] = true;

        const directionVectors = [[-1, 0], [1, 0], [0, -1], [0, 1]];
        const numberOfDirections = directionVectors.length;
        let directionIndexTracker = 0;
        while (directionIndexTracker < numberOfDirections) {
            const currentDirectionVector = directionVectors[directionIndexTracker];
            const nextRowCoordinate = currentRow + currentDirectionVector[0];
            const nextColumnCoordinate = currentColumn + currentDirectionVector[1];

            const isRowValid = nextRowCoordinate >= 0 && nextRowCoordinate < totalRows;
            const isColumnValid = nextColumnCoordinate >= 0 && nextColumnCoordinate < totalColumns;

            if (isRowValid && isColumnValid && gridHeights[nextRowCoordinate][nextColumnCoordinate] >= gridHeights[currentRow][currentColumn]) {
                exploreOceanFlow(nextRowCoordinate, nextColumnCoordinate, gridHeights, oceanPathGrid);
            }
            directionIndexTracker++;
        }
    }

    let pacificRowBorderIndex = 0;
    while (pacificRowBorderIndex < totalRows) {
        exploreOceanFlow(pacificRowBorderIndex, 0, heights, pacificReachableCells);
        pacificRowBorderIndex++;
    }

    let pacificColumnBorderIndex = 0;
    while (pacificColumnBorderIndex < totalColumns) {
        exploreOceanFlow(0, pacificColumnBorderIndex, heights, pacificReachableCells);
        pacificColumnBorderIndex++;
    }

    let atlanticRowBorderIndex = 0;
    while (atlanticRowBorderIndex < totalRows) {
        exploreOceanFlow(atlanticRowBorderIndex, totalColumns - 1, heights, atlanticReachableCells);
        atlanticRowBorderIndex++;
    }

    let atlanticColumnBorderIndex = 0;
    while (atlanticColumnBorderIndex < totalColumns) {
        exploreOceanFlow(totalRows - 1, atlanticColumnBorderIndex, heights, atlanticReachableCells);
        atlanticColumnBorderIndex++;
    }

    let finalRowIterator = 0;
    while (finalRowIterator < totalRows) {
        let finalColumnIterator = 0;
        while (finalColumnIterator < totalColumns) {
            if (pacificReachableCells[finalRowIterator][finalColumnIterator] && atlanticReachableCells[finalRowIterator][finalColumnIterator]) {
                waterFlowResult.push([finalRowIterator, finalColumnIterator]);
            }
            finalColumnIterator++;
        }
        finalRowIterator++;
    }

    return waterFlowResult;
};