Your country has an infinite number of lakes. Initially, all the lakes are empty, but when it rains over the nth lake, the nth lake becomes full of water. If it rains over a lake that is full of water, there will be a flood. Your goal is to avoid flo

avoidFlood.js

/**
 * @param {number[]} rains
 * @return {number[]}
 */
var avoidFlood = function(rains) {
    const n = rains.length;
    const ans = new Array(n).fill(1); // default dry days to lake 1 (will be overwritten)
    const fullLakes = new Map(); // maps lake number to the day it was last filled
    const dryDays = []; // stores indices of dry days

    for (let i = 0; i < n; i++) {
        const lake = rains[i];

        if (lake > 0) {
            // It's raining on lake `lake`
            ans[i] = -1;

            if (fullLakes.has(lake)) {
                // Lake is already full - we need to dry it before today
                let dried = false;

                for (let j = 0; j < dryDays.length; j++) {
                    if (dryDays[j] > fullLakes.get(lake)) {
                        // We can dry this lake on dryDays[j]
                        ans[dryDays[j]] = lake;
                        dryDays.splice(j, 1); // remove used dry day
                        dried = true;
                        break;
                    }
                }

                if (!dried) return []; // flood is unavoidable
            }

            fullLakes.set(lake, i); // mark lake as full
        } else {
            // It's a dry day - store the index for later use
            dryDays.push(i);
        }
    }

    return ans;
};