# 43ms C++ solution--concise and easy to understand

• class Solution {
public:
int shortestDistance(vector<vector<int>>& grid) {
if (grid.empty() || grid[0].empty()) {
return -1;
}
int m = grid.size(), n = grid[0].size(), res = INT_MAX, target = 0;
vector<vector<int>> sum(m, vector<int>(n, 0));
vector<vector<int>> dirs{{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
if (grid[i][j] == 1) {
vector<vector<int>> dist(m, vector<int>(n, 0));
queue<pair<int, int>> q;
q.push(make_pair(i, j));
while (!q.empty()) {
int x = q.front().first;
int y = q.front().second;
q.pop();
for (auto &dir : dirs) {
int nx = x + dir[0];
int ny = y + dir[1];
if (nx >= 0 && nx < m && ny >= 0 && ny < n && grid[nx][ny] == target) {
q.push(make_pair(nx, ny));
--grid[nx][ny];
dist[nx][ny] = dist[x][y] + 1;
sum[nx][ny] += dist[nx][ny];
}
}
}
--target;
}
}
}
for (int i = 0; i < m; ++i) {
for (int j = 0; j < n; ++j) {
if (grid[i][j] == target) {
res = min(res, sum[i][j]);
}
}
}
return res == INT_MAX ? -1 : res;
}
};

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