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fix: optimise: eliminate explicit graph

This commit is contained in:
eat-swap 2022-04-29 01:15:55 +08:00
parent 2a3854e094
commit 3a25345149
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GPG Key ID: 8C089CB1A2B7544F
1 changed files with 8 additions and 16 deletions
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24
cpp/2204/220428.cpp
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@ -64,26 +64,15 @@ public:
*/
class Solution {
private:
static inline int dX[] = {0, 1, 0, -1};
static inline int dY[] = {1, 0, -1, 0};
public:
static int minimumEffortPath(const std::vector<std::vector<int>>& heights) {
const std::size_t m = heights.size(), n = heights.front().size(), total = m * n;
std::vector<int> d(total, 0x7FFFFFFF);
std::vector<std::vector<int>> G(total);
std::vector<bool> vis(total);
for (int i = 0; i < m * n; ++i) {
// Build graph
if (i + n < total) {
// Down
G[i].push_back(i + n);
G[i + n].push_back(i);
}
if ((i + 1) % n) {
// Right
G[i].push_back(i + 1);
G[i + 1].push_back(i);
}
}
// Pair <Dist, Node#>
std::priority_queue<std::pair<int, int>, std::vector<std::pair<int, int>>, std::greater<>> q;
@ -99,8 +88,11 @@ public:
continue;
vis[idx] = true;
for (int idxNext : G[idx]) {
int length = std::abs(heights[idx / n][idx % n] - heights[idxNext / n][idxNext % n]);
for (int i = 0; i < 4; ++i) {
const int xNext = dX[i] + (idx / n), yNext = dY[i] + (idx % n);
if (xNext < 0 || xNext >= m || yNext < 0 || yNext >= n)
continue;
const int idxNext = xNext * n + yNext, length = std::abs(heights[idx / n][idx % n] - heights[idxNext / n][idxNext % n]);
if (d[idxNext] > std::max(d[idx], length)) {
d[idxNext] = std::max(d[idx], length);
q.push({d[idxNext], idxNext});