洛谷P1902 刺杀大使

题目

二分加广搜

#include <bits/stdc++.h>
using namespace std;
int n, m, l, r, p[1001][1001], vis[1001][1001];
int dx[6] = {0, 1, -1, 0, 0};
int dy[6] = {0, 0, 0, 1, -1};
int qx[100100], qy[1001001]; 
bool check(int d)
{
	memset(vis, 0, sizeof(vis));
	int front = 0, tail = 0;
	for (int i = 1; i <= m; i++)
		qx[++tail] = i, qy[tail] = 1;
	int tot = 0;
	while (front <= tail)
	{
		int nx = qx[front], ny = qy[front++];
		if (ny == n)
			tot++;
		for (int i = 1; i <= 4; i++)
		{
			int ax = nx + dx[i];
			int ay = ny + dy[i];
			if (p[ay][ax] <= d && !vis[ay][ax] && (ax <= m && ax >= 1 && ay <= n && ay >= 1))
				qx[++tail] = ax, qy[tail] = ay, vis[ay][ax] = 1;
		}
	}
	if (tot == m) return 1;
	return 0;
}
int main()
{
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= n; i++)
		for (int j = 1; j <= m; j++)
			scanf("%d", &p[i][j]), r = max(r, p[i][j]);
	int mid = 0, ans = 0;

	while (l <= r)
	{
		mid = (l + r) >> 1;
		if (check(mid))
			ans = mid, r = mid - 1;
		else l = mid + 1;
	}
	printf("%d", ans);
	return 0;
}