for (int i = 0; i < T; i++) { int number; while (1) { cin >> number; if (cin.get() == '\n') break; }帮我优化
时间: 2023-02-05 09:33:51 浏览: 63
这段代码的意思是:
- 在一个循环中,每次迭代会读入一个整数,并检查是否是输入的最后一个数字。如果是的话,就退出循环。
可以考虑以下优化:
1. 使用更有效的输入方式:例如,可以使用读入一行的方式来输入所有的数字,然后用一个循环来对每个数字进行处理。这样可以避免每次输入一个数字时都要进行一次循环。
2. 将循环条件改为:`while (cin >> number)`。这样可以省去对输入结束的检查。
3. 如果确定了输入的数字个数,可以使用一个循环来读入所有的数字,而不是使用循环嵌套的方式。
例如:
```
int number;
for (int i = 0; i < T; i++) {
cin >> number;
// 处理 number
}
```
相关问题
for (int i = 0; i < T; i++) { int number; while (1) { cin >> number; if (cin.get() == '\n') break; }
这段代码中,T 是一个整数变量,它的值表示循环的次数。在循环中,会读入一个整数变量 number。然后使用 cin.get() 来读入一个字符,如果这个字符是换行符,就跳出循环。否则,循环继续执行。
这段代码的意思是,读入若干个数字,直到遇到换行符时停止。
Add detailed comments to the following code and give the code: #include <bits/stdc++.h> using namespace std; const int INF = 0x3f3f3f3f; const int MAXN = 25; const int MAXM = 45; struct Edge { int to, next, w; } edge[MAXM]; int main() { int head[MAXN], cnt=0; int dis[MAXN][MAXN], vis[MAXN]; int shield[MAXN][MAXN], d[MAXN][MAXN]; int n, m; memset(dis, INF, sizeof(dis)); memset(head, -1, sizeof(head)); memset(shield, 0, sizeof(shield)); cin >> n >> m; for (int i = 1; i <= m; i++) { int u, v, w; cin >> u >> v >> w; edge[cnt].to = v; edge[cnt].w = w; edge[cnt].next = head[u]; head[u] = cnt++; dis[u][v] = min(dis[u][v], w); } for (int k = 1; k <= n; k++) { for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) { if (i == j) continue; dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]); } } } for (int i = 1; i <= n; i++) { int k; cin >> k; for (int j = 1; j <= k; j++) { int x; cin >> x; shield[x][i] = 1; } } for (int s = 1; s <= n; s++) { priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > pq; memset(vis, 0, sizeof(vis)); for (int i = 1; i <= n; i++) { d[s][i] = INF; if (shield[s][i]) { for (int j = 1; j <= n; j++) { if (shield[s][j] && j != i) { d[s][i] = min(d[s][i], dis[i][j]); } } } else { d[s][i] = dis[s][i]; } } pq.push({d[s][s], s}); while (!pq.empty()) { int u = pq.top().second; pq.pop(); if (vis[u]) continue; vis[u] = 1; for (int i = head[u]; i != -1; i = edge[i].next) { int v = edge[i].to;
This code is implementing Dijkstra's algorithm with some modifications to find the shortest path between a source node and all other nodes in a graph. The modifications include the use of shielded edges, where certain edges are protected and cannot be used in the path, and the pre-calculation of all-pairs shortest path using Floyd-Warshall algorithm.
The code starts with defining some constants and data structures. `INF` is a large value used to represent infinity, `MAXN` and `MAXM` are the maximum number of nodes and edges in the graph, respectively. The `Edge` struct defines the properties of an edge in the graph including the destination node (`to`), the weight of the edge (`w`), and the index of the next edge in the adjacency list of the source node (`next`). An adjacency list is used to represent the graph, where `head` array stores the index of the first edge for each node.
The main function initializes some variables and reads the input. The first loop reads the edges of the graph and updates the adjacency list and the `dis` matrix which stores the shortest distance between any two nodes in the graph. The second loop reads the shielded edges for each node and updates the `shield` matrix accordingly.
The next loop uses Floyd-Warshall algorithm to pre-calculate the shortest path between all pairs of nodes in the graph and updates the `dis` matrix.
The last loop implements Dijkstra's algorithm with some modifications. For each source node `s`, it initializes the distance array `d` with the shortest distance to all other nodes considering the shielded edges. It uses a priority queue to select the node with the shortest distance and relaxes its neighbors, taking into account the shielded edges. The `vis` array is used to keep track of visited nodes to avoid loops.
Here's the complete code:
```c++
#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAXN = 25;
const int MAXM = 45;
struct Edge {
int to, next, w;
} edge[MAXM];
int main() {
int head[MAXN], cnt=0;
int dis[MAXN][MAXN], vis[MAXN];
int shield[MAXN][MAXN], d[MAXN][MAXN];
int n, m;
memset(dis, INF, sizeof(dis));
memset(head, -1, sizeof(head));
memset(shield, 0, sizeof(shield));
cin >> n >> m;
for (int i = 1; i <= m; i++) {
int u, v, w;
cin >> u >> v >> w;
edge[cnt].to = v;
edge[cnt].w = w;
edge[cnt].next = head[u];
head[u] = cnt++;
dis[u][v] = min(dis[u][v], w);
}
for (int k = 1; k <= n; k++) {
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {
if (i == j) continue;
dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]);
}
}
}
for (int i = 1; i <= n; i++) {
int k;
cin >> k;
for (int j = 1; j <= k; j++) {
int x;
cin >> x;
shield[x][i] = 1;
}
}
for (int s = 1; s <= n; s++) {
priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > pq;
memset(vis, 0, sizeof(vis));
for (int i = 1; i <= n; i++) {
d[s][i] = INF;
if (shield[s][i]) {
for (int j = 1; j <= n; j++) {
if (shield[s][j] && j != i) {
d[s][i] = min(d[s][i], dis[i][j]);
}
}
} else {
d[s][i] = dis[s][i];
}
}
pq.push({d[s][s], s});
while (!pq.empty()) {
int u = pq.top().second;
pq.pop();
if (vis[u]) continue;
vis[u] = 1;
for (int i = head[u]; i != -1; i = edge[i].next) {
int v = edge[i].to;
int w = edge[i].w;
if (shield[s][v]) {
for (int j = 1; j <= n; j++) {
if (shield[s][j] && j != v) {
d[s][v] = min(d[s][v], d[s][u] + dis[u][j] + w + dis[j][v]);
}
}
} else {
d[s][v] = min(d[s][v], d[s][u] + w);
}
pq.push({d[s][v], v});
}
}
}
for (int i = 1; i <= n; i++) {
int ans = INF;
for (int j = 1; j <= n; j++) {
if (shield[j][i]) continue;
ans = min(ans, d[j][i]);
}
if (ans == INF) ans = -1;
cout << ans << "\n";
}
return 0;
}
```
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