和你想法一样，实现有点不同：

#include <stdio.h>

#define N 100005

int main(void)
{
    int t;

    scanf("%d", &t);

    while (t--) {
        int i, n, num[N];

        scanf("%d", &n);

        for (i = 0; i < n; i++)
            scanf("%d", num + i);

        int left = 0, right = n - 1, res = 0, counted = 0;

        while (right > left) {
            int min = num[left] < num[right] ? num[left] : num[right];

            if (min > counted) {
                res += (min - counted) * (right - left);
                counted = min;
            }
            if (num[left] < num[right])
                left++;
            else
                right--;
        }
        printf("%d\n", res);
    }

    return 0;
}