Campus Bike II | TOP DOWN DP

public int assignBikesMethod3(int[][] workers, int[][] bikes) {
    int dpTable[][] = new int[workers.length][1 << bikes.length];
    for (int[] dpRow : dpTable) {
        Arrays.fill(dpRow, -1);
    }
    return assignBikesMethod3(workers, bikes, 0, new BitMask(0), dpTable);
}

public int assignBikesMethod3(int[][] workers, int[][] bikes, int worker, BitMask assignedBikes, int dp[][]) {
    if (worker == workers.length) return 0;
    if (dp[worker][assignedBikes.getMask()] != -1) {
        return dp[worker][assignedBikes.getMask()];
    }
    int ans = MAX_VALUE;
    for (int i = 0; i < bikes.length; i++) {
        if (!assignedBikes.checkSetBit(i)) {
            assignedBikes.setBit(i);
            int distance = manhattanDistance(workers[worker], bikes[i]);
            ans = min(ans, distance + assignBikesMethod3(workers, bikes, worker + 1, assignedBikes, dp));
            assignedBikes.flip(i);
        }
    }
    return dp[worker][assignedBikes.getMask()] = ans;
}
class BitMask {
    int val;

    public BitMask(int val) {
        this.val = val;
    }

    public void setBit(int bitIndex) {
        val |= 1 << bitIndex;
    }

    public void flip(int bitIndex) {
        val = val ^ (1 << bitIndex);
    }

    boolean checkSetBit(int bitIndex) {
        return (val & (1 << bitIndex)) >= 1;
    }

    public int getMask() {
        return val;
    }
}