【力扣九日】day4

1.重新排列数组 力扣1470

class Solution {
    public int[] shuffle(int[] nums, int n) {
        int [] res = new int[2*n];
        for(int i = 0;i < n;i++)
        {
            res[2*i] = nums[i];
            res[2*i+1] = nums[n+i];
        }
        return res;

    }
}

2.数组串联 力扣1929

class Solution {
    public int[] getConcatenation(int[] nums) {
        int[] ans = new int[nums.length*2];
        int n = nums.length;
        for(int i=0;i<nums.length;i++){
            ans[i] = nums[i];
            ans[i + n] = nums[i];
        }
        return ans;


    }
}

3.基于排列构建数组 力扣1920

class Solution {
    public int[] buildArray(int[] nums) {
        int[] ans = new int[nums.length];
        for(int i = 0;i < nums.length;i++){
            ans[i] = nums[nums[i]];
        }
        return ans;

    }
}

4.维数组的动态和 力扣1480

class Solution {
    public int[] runningSum(int[] nums) {
       int n = nums.length;
        int[] ans = new int[n];
        for (int i = 0, s = 0; i < n; i++) {
            ans[i] = s = s + nums[i];
        }
        return ans;
        }
       }

5.左旋字符串 剑指offer56

class Solution {
    public String reverseLeftWords(String s, int n) {
        String a = "";
        for(int i = n;i < n + s.length();i++){
            a += s.charAt(i % s.length());
        }
        return a;

    }
}

6.IP 地址无效化 力扣1108
直接用+连接字符串

class Solution {
    public String defangIPaddr(String address) {
        String s = "";
        for(int i = 0;i < address.length();i++){
            if(address.charAt(i) == '.'){
                s += "[.]";
            }
            else s += address.charAt(i);
        }
        return s;

    }
}

7.替换空格 剑指05

class Solution {
    public String replaceSpace(String s) {
        String ans = "";
        for(int i = 0;i < s.length();i++){
            if(s.charAt(i) == ' '){
                ans += "%20";
            }
            else ans += s.charAt(i);
        }
        return ans;
        

    }
}

8.有多少小于当前数字的数字 力扣1365

class Solution {
    public int[] smallerNumbersThanCurrent(int[] nums) {
        int[] a = new int[nums.length];

        for(int i = 0;i < nums.length;i++){
            a[i] = 0;
            for(int j = 0;j < nums.length;j++){
                if(nums[i] > nums[j]){
                    a[i]++;
                }
            }

        }
        return a;

    }
}

9.打印从1到最大数 剑指17
pow方法是求a的b次幂

class Solution {
    public int[] printNumbers(int n) {
        int e = (int)Math.pow(10,n) - 1;
        int[] a = new int[e];
        for(int i = 0;i < a.length;i++){
            a[i] = i + 1;
        }
        return a;

    }
}