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<cstdio>
#include<algorithm>
#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;
}