刷题之Implement strStr()、Climbing Stairs

public class Solution {
    public int strStr(String haystack, String needle) {
        int big = haystack.length();
        int sub = needle.length();
        if(big==0 && sub==0) return 0;
        if(big==0 && sub!=0) return -1;
        int index = big-sub;
        for(int i=0;i<=index;i++){
            if(haystack.substring(i,sub+i).equals(needle))return i;
        }
        return -1;
    }
}

 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）：

public class Solution {
    public int climbStairs(int n) {
        if(n<1)return 0;
        if(n==1)return 1;
        if(n==2)return 2;
        return climbStairs(n-1)+climbStairs(n-2);
    }
}

2）类似斐波那契数列，开头1,2.代替1.1

public class Solution {
    public int climbStairs(int n) {
        if(n<1)return 0;
        if(n==1)return 1;
        if(n==2)return 2;
        int nums = 0;
        int one = 1;
        int two = 2;
        for(int i=3;i<=n;i++){
            nums = one+two;
            one = two;
            two = nums;
        }
        return nums;
    }
}

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