# x 417. Pacific Atlantic Water Flow

```jsx
/**
 * @param {number[][]} heights
 * @return {number[][]}
 */

let memo;
var pacificAtlantic = function (heights) {
    memo = new Array(heights.length);
    for (let i = 0; i < heights.length; i++) {
        memo[i] = new Array(heights[0].length).fill(0);
    }

    const answer = [];
    for (let i = 0; i < heights.length; i++) {
        for (let j = 0; j < heights[0].length; j++) {
            const [f, s] = traverse(heights, memo, i, j);
            if (f && s) {
                memo[i][j] = 1;
                answer.push([i, j]);
            } else {
                memo[i][j] = -1;
            }
        }
    }

    return answer;
};

function traverse(m, memo, row, col, prev = 100001) {
    if (row < 0 || col < 0) {
        return [true, false];
    }
    if (row >= m.length || col >= m[0].length) {
        return [false, true];
    }

    const curr = m[row][col];
    if (curr < 0) return [false, false];
    if (curr > prev) return [false, false];

    if (memo[row][col] === 1) return [true, true];

    m[row][col] -= 200000;

    const left = traverse(m, memo, row, col - 1, curr);
    const up = traverse(m, memo, row - 1, col, curr);
    const right = traverse(m, memo, row, col + 1, curr);
    const down = traverse(m, memo, row + 1, col, curr);
    m[row][col] += 200000;

    const pacific = left[0] || up[0] || right[0] || down[0];
    const atlantic = left[1] || up[1] || right[1] || down[1];

    return [pacific, atlantic];
}
```


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