昨天的 arc177_c，从标程里第一次知道 tuple 这个东西，但是发生了一个奇怪的事

我如果写成这样

q.push(make_tuple(sx, sy, 0));

q.push(make_tuple(tx, ty, dist[tx][ty]));

并这样调用

int x = get<0>(q.top()), y = get<1>(q.top());

输出来的 dist 矩阵就是这样

5
RBRBB
RBRRR
RRRBR
RBBRB
BBRBR
0 1 1 2 2
0 1 0 1 1
0 0 0 1 1
0 1 1 1 2
1 2 1 2 2
2 1 1 0 0
2 1 2 1 1
3 2 2 1 2
3 2 2 2 2
2 2 3 2 3
4

第一个图就发生错误计算，为什么？

且改成形如 {dist[x][y], x, y}，把 dist 放前边，坐标调用 get<1> 和 get<2> 就又正常了？

附：

#include <bits/stdc++.h>
#define re register int 
using namespace std;
typedef tuple<int, int, int> tp;
const int N = 510, inf = 0x3f3f3f3f;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, 1, 0, -1};
char g[N][N];
int n, res1, res2, dist[N][N];
bool vis[N][N];
priority_queue< tp, vector<tp>, greater<tp> > q;

inline int work(int sx, int sy, int ex, int ey, char c)
{
	memset(vis, false, sizeof(vis));
	for (re i = 1; i <= n; i ++)
		for (re j = 1; j <= n; j ++) dist[i][j] = inf;
		
	dist[sx][sy] = 0;
	q.push(make_tuple(sx, sy, 0));
	
	while (!q.empty())
	{
		int x = get<0>(q.top()), y = get<1>(q.top());
		q.pop();
		if (vis[x][y]) continue;
		vis[x][y] = true;
		
		for (re i = 0; i < 4; i ++)
		{
			int tx = x + dx[i], ty = y + dy[i];
			if (tx < 1 || tx > n || ty < 1 || ty > n) continue;
			
			int w = (g[tx][ty] == c ? 0 : 1);
			if (dist[x][y] + w < dist[tx][ty])
			{
				dist[tx][ty] = dist[x][y] + w;
				q.push(make_tuple(tx, ty, dist[tx][ty]));
			}
		}
	}
/*	
	for (re i = 1; i <= n; i ++)
	{
		for (re j = 1; j <= n; j ++) cout << dist[i][j] << ' ';
		cout << '\n';
	}	
*/	
	return dist[ex][ey];
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	
	cin >> n;
	for (re i = 1; i <= n; i ++)
		for (re j = 1; j <= n; j ++) cin >> g[i][j];
	res1 = work(1, 1, n, n, 'R');
	res2 = work(1, n, n, 1, 'B');
	
	cout << res1 + res2 << '\n';
	
	return 0;
}