刷题之Implement strStr()、Climbing Stairs

 1 public class Solution {
 2     public int strStr(String haystack, String needle) {
 3         int big = haystack.length();
 4         int sub = needle.length();
 5         if(big==0 && sub==0) return 0;
 6         if(big==0 && sub!=0) return -1;
 7         int index = big-sub;
 8         for(int i=0;i<=index;i++){
 9             if(haystack.substring(i,sub+i).equals(needle))return i;
10         }
11         return -1;
12     }
13 }

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是int index = haystack.indexOf(needle)的另一种做法

Climbing Stairs

1）递归调用（容易内存溢出）：

1 public class Solution {
2     public int climbStairs(int n) {
3         if(n<1)return 0;
4         if(n==1)return 1;
5         if(n==2)return 2;
6         return climbStairs(n-1)+climbStairs(n-2);
7     }
8 }

2）类似斐波那契数列，开头1,2.代替1.1

 1 public class Solution {
 2     public int climbStairs(int n) {
 3         if(n<1)return 0;
 4         if(n==1)return 1;
 5         if(n==2)return 2;
 6         int nums = 0;
 7         int one = 1;
 8         int two = 2;
 9         for(int i=3;i<=n;i++){
10             nums = one+two;
11             one = two;
12             two = nums;
13         }
14         return nums;
15     }
16 }

https://leetcode.com/problems/climbing-stairs/#/description