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1. What does this program print? It counts islands with four-way moves, where 1 is land and 0 is water. ``

cpp
#include <iostream>
#include <string>
#include <vector>

std::vector<std::string> g = {"110", "011", "100", "001"};

void sink(int r, int c) {
    if (r < 0 || r >= 4 || c < 0 || c >= 3 || g[r][c] != '1') return;
    g[r][c] = '0';
    sink(r - 1, c);
    sink(r + 1, c);
    sink(r, c - 1);
    sink(r, c + 1);
}

int main() {
    int count = 0;
    for (int r = 0; r < 4; ++r)
        for (int c = 0; c < 3; ++c)
            if (g[r][c] == '1') {
                ++count;
                sink(r, c);
            }
    std::cout << count << '\n';
}

``

3246

2. What does this program print? ``

cpp
#include <iostream>
#include <string>

int main() {
    int keys = 0;
    for (char ch : std::string("ace")) keys |= 1 << (ch - 'a');
    std::cout << keys << ' ' << (keys & (1 << ('c' - 'a'))) << ' ' << (keys & (1 << ('b' - 'a'))) << '\n';
}

``

21 2 021 4 07 4 021 4 2

3. In floodFill, the first lines are char oldColor = g[sr][sc]; and if (oldColor == newColor) return;. What happens if that guard is removed and the fill is called with the same colour twice?

It repaints only the start cell and then stopsThe program stops with a segmentation fault at onceIt repaints every cell in the grid, not just the connected regionIt never ends, because a repainted neighbour still matches the old colour and is queued again

4. The lesson's third maze gives 6 when the visited index includes the key set. Which change makes the same maze return -1?

Marking a state visited when it is popped, not when it is pushedReturning the steps when the bag holds any one key, not every keyIgnoring the key set in the visited index, so each cell is marked once whatever keys are held

5. The grid below has three land cells. How many islands does it have with four-way moves, and how many with eight-way moves? ``

text
110
001

``

2 and 22 and 11 and 11 and 2

Grid search and state BFS