从左往右扫描一遍， 得从每个位置往右伸长不会碰到天花板的高度， 右往左一样， 取最小， 然后就是可以放“水”的高度了

#include
    
     #include
     
      #define REP(i, a, b) for(int i = (a); i < (b); i++)using namespace std;const int MAXN = 1123456;int p[MAXN], s[MAXN], h[MAXN], n; int main(){	int T;	scanf("%d", &T);		while(T--)	{		scanf("%d", &n);		REP(i, 0, n) scanf("%d", &p[i]);		REP(i, 0, n) scanf("%d", &s[i]);				int level = s[0]; 		REP(i, 0, n)		{			if(p[i] > level) level = p[i];			if(s[i] < level) level = s[i];			h[i] = level;		}				int ans = 0;		level = s[n-1];		for(int i = n - 1; i >= 0; i--)		{		    if(p[i] > level) level = p[i];			if(s[i] < level) level = s[i];			ans += min(level, h[i]) - p[i];		}		printf("%d\n", ans);	}		return 0;}