如何在三重嵌套循环中计算频率计数

Question

我正在尝试确定三重嵌套循环的频率计数。

for i = 1 to n do
    for j = 1 to i do
        for k = i to j do
            x =  x + 1

我知道在我达到n 的值之前，语句x = x + 1不会被执行

有什么关于如何开始的提示/建议吗？

Answer 1

让我们以4和5为例。当i=4时，

...
    for j = 1 to 4 do
        for k = 4 to j do
            x =  x + 1
...j = 1
   for k = 4 to 1 do  // 4 times
       x =  x + 1
...j = 2
   for k = 4 to 2 do  // 3 times
       x =  x + 1
...j = 3
   for k = 4 to 3 do   // twice
       x =  x + 1
...j = 4
   for k = 4 to 4 do   // once
       x =  x + 1

当i=5时，

...
    for j = 1 to 5 do
        for k = 5 to j do
            x =  x + 1
...j = 1
   for k = 5 to 1 do  // 5 times
       x =  x + 1
...j = 2
   for k = 5 to 2 do  // 4 times
       x =  x + 1
...j = 3
   for k = 5 to 3 do   // 3 times
       x =  x + 1
...j = 4
   for k = 5 to 4 do   // twice
       x =  x + 1
...j = 5
   for k = 5 to 5 do   // once
       x =  x + 1

模式？