計算到達第 n 級臺階的方法
有 n 個臺階。一個人將從第一級臺階走到第 n 級臺階。也提供了此人每一步最多可以跨越的臺階數。在此資訊的基礎上,我們必須找到到達第 n 級臺階的可能途徑。
假設一個人每一步最多可以跨兩個臺階。因此我們可找到遞迴關係來解決此問題。一個人可以從第 n-1 個臺階或從第 n-2 個臺階走到第 n 個臺階。因此 ways(n) = ways(n-1) + ways(n-2)。
輸入和輸出
Input: The number of stairs, say 10 the maximum number of stairs that can be jumped in one step, say 2 Output: Enter number of stairs: 10 Enter max stair a person can climb: 2 Number of ways to reach: 89
演算法
stairClimpWays(stair, max)
輸入 − 臺階數,單次跨越的最大臺階數。
輸出 − 能夠到達的可能途徑數。
Begin define array count of size same as stair number count[0] := 1 count[0] := 1 for i := 2 to stair -1, do count[i] := 0 for j = 1 to i and j <= max; do count[i] := count[i] + count[i - j] done done return count[stair - 1] End
示例
#include<iostream>
using namespace std;
int stairClimbWays(int stair, int max) {
int count[stair]; //fill the result stair using bottom up manner
count[0] = 1; //when there are 0 or 1 stair, 1 way to climb
count[1] = 1;
for (int i=2; i<stair; i++) { //for stair 2 to higher
count[i] = 0;
for(int j=1; j<=max && j<=i; j++)
count[i] += count[i-j];
}
return count[stair-1];
}
int countWays(int stair, int max) { //person can climb 1,2,...max stairs at a time
return stairClimbWays(stair+1, max);
}
int main () {
int stair, max;
cout << "Enter number of stairs: "; cin >> stair;
cout << "Enter max stair a person can climb: "; cin >> max;
cout << "Number of ways to reach: " << countWays(stair, max);
}輸出
Enter number of stairs: 10 Enter max stair a person can climb: 2 Number of ways to reach: 89
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