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package leetcode;
/**
* leetcode_70 You are climbing a stair case. It takes n steps to reach to the
* top.
*
* Each time you can either climb 1 or 2 steps. In how many distinct ways can
* you climb to the top?
*
*
* solution.
*
* 1.计算有多少种2的情况，比如一个2，其他都是1；10个2，其他都是1 .
*
* 2.计算每种情况的可能排列情况.
*
* 上面的算法解决不了问题.
*
* 分析算法，归结为斐波那契数列.
*
* @author rwxn
*
*/
public class java_70 {
public int climbStairs(int n) {
int[] count = new int[n + 3];
if (n == 1)
return 1;
if (n == 2)
return 2;
count[0] = 1;
count[1] = 1;
count[2] = 2;
for (int i = 3; i <= n; ++i)
count[i] = count[i - 1] + count[i - 2];
return count[n];
}
}
// public int climbStairs(int n) {
// int result = 0;
// if (n == 0 || n == 1) {
// return 1;
// }
//
// for (int count = n / 2; count >= 0; count--) {
// result = result + arrangement(n - count, count);
// }
// return result;
// }
//
// public int arrangement(int n, int m) {// 排列C
// int result = 0;
// long fenzi = 1, fenmu_1 = 1,fenmu_2 = 1;
// if (n == m || m == 0) {
// return result = 1;
// }
//
// for(int i = n;i>=0;i--){
// if(i == 0){
// fenzi = fenzi * 1;
// }else {
// fenzi = fenzi*i;
// }
// }
// for(int i = m;i>0;i--){
// fenmu_1 = fenmu_1*i;
// }
// for(int i =n- m;i>0;i--){
// fenmu_2 = fenmu_2*i;
// }
// System.out.println(fenzi/(fenmu_1*fenmu_2));
// result = (int)(fenzi/(fenmu_1*fenmu_2));
//
//
//// if (n - m == m && m == 1) {
//// result = 2;
//// } else if (n - m > m) {
////
//// for (int i = n - m + 1; i <= n; i++) {
//// fenzi = fenzi * i;
//// }
//// for (int i = m; i >= 1; i--) {
//// fenmu = fenmu * i;
//// }
//// // result = (int) Math.floor(fenzi / fenmu);
//// result = (int) (fenzi / fenmu);
//// } else{
//// for (int i = m + 1; i < n; i++) {
//// fenzi = fenzi * i;
//// }
//// for (int i = n - m; i >= 1; i--) {
//// fenmu = fenmu * i;
//// }
//// result = (int) (fenzi / fenmu);
//// }
//
// return result;
// }