題目←

總覺得spfa一臉可做的樣子然而過不了
于是乖乖打了二分+驗證

#include<iostream> #include<cstdio> #include<queue> #include<cstring> #include<algorithm> using namespace std; const int MAXN = 1000 + 50; int mr[] = {0,1,-1,0},mu[] = {1,0,0,-1}; bool used[MAXN][MAXN]; int n,m; bool in(int x,int y){if(x < 1 || y < 1)return false;if(x > n || y > m)return false;return true; } int lim; int map[MAXN][MAXN]; struct zt{int x,y; }; queue <zt> q; bool C(){memset(used,0,sizeof(used));while(!q.empty())q.pop();for(int i = 1;i <= m;i ++){q.push((zt){1,i});used[1][i] = true;}while(!q.empty()){zt u = q.front();q.pop();for(int i = 0;i <= 3;i ++){int x = u.x + mu[i];int y = u.y + mr[i]; if(x < 1 || y < 1 || x > n || y > m || used[x][y] || map[x][y] > lim)continue;q.push((zt){x,y});used[x][y] = true;if(x == n){return true;}}}return false; } int lin[MAXN*MAXN],tot,maxx,L,R; int main(){scanf("%d%d",&n,&m);for(int i = 1;i <= n;i ++){for(int j = 1;j <= m;j ++){scanf("%d",&map[i][j]);lin[++ tot] = map[i][j];}}sort(lin + 1,lin + tot + 1);tot = unique(lin + 1,lin + tot + 1) - lin - 1;L = -1;R = tot + 1;while(R - L > 1){int mid = R + L >> 1;lim = lin[mid];if(C())R = mid;else L = mid;}printf("%d",lin[R]); }

總結

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