《LeetCode力扣练习》代码随想录——数组（长度最小的子数组---Java）

《LeetCode力扣练习》代码随想录——数组（长度最小的子数组—Java）

刷题思路来源于代码随想录

209. 长度最小的子数组

滑动窗口——O(n)

class Solution {
    public int minSubArrayLen(int target, int[] nums) {

        if(nums.length==1){
            return nums[0]>=target?1:0;
        }

        int slow=0;
        int fast=0;
        int sum=0;
        int result=Integer.MAX_VALUE;

        for(;fast<nums.length;fast++){

            sum+=nums[fast];

            while(sum>=target){

                int temp=fast-slow+1;
                result=temp<result?temp:result;
                sum-=nums[slow++];

            }

        }

        return result==Integer.MAX_VALUE?0:result;

    }
}

前缀和 + 二分查找——O(n log(n))

class Solution {
    public int minSubArrayLen(int target, int[] nums) {

        if(nums.length==0){
            return 0;
        }

        int[] sum=new int[nums.length+1];
        int result=Integer.MAX_VALUE;

        for(int i=1;i<nums.length+1;i++){
            sum[i]=sum[i-1]+nums[i-1];
        }

        for(int i=1;i<nums.length+1;i++){

            int newTarget=target+sum[i-1];

            int location=binarySearch(newTarget,sum);

            if(location<0){
                location=-(location+1);
            }

            int temp=location-(i-1);

            if(location<=nums.length){
                result=result<temp?result:temp;
            }

        }

        return result==Integer.MAX_VALUE?0:result;

    }

    public int binarySearch(int target, int[] nums){

        if(nums.length==0){
            return -1;
        }

        int left=0;
        int right=nums.length-1;

        while(left<=right){

            int middle=(left+right)>>>1;

            if(nums[middle]>target){
                right=middle-1;
            }else if(nums[middle]<target){
                left=middle+1;
            }else{
                return middle;
            }

        }

        return -left-1;

    }
}

904. 水果成篮

滑动窗口——O(n)

class Solution {
    public int totalFruit(int[] fruits) {

        if(fruits.length==1){
            return 1;
        }

        int slow=0;
        int fast=0;

        int[] map=new int[fruits.length];
        int size=0;
        int result=Integer.MIN_VALUE;

        for(;fast<fruits.length;fast++){

            if(map[fruits[fast]]==0){
                size++;
            }

            map[fruits[fast]]++;

            while(size>2){

                map[fruits[slow]]--;

                if(map[fruits[slow]]==0){
                    size--;
                }

                slow++;

            }

            int temp=fast-slow+1;

            result=result<temp?temp:result;

        }

        return result==Integer.MIN_VALUE?0:result;

    }
}

76. 最小覆盖子串

滑动窗口——O(n+m)

正常的常规写法

class Solution {
    public String minWindow(String s, String t) {

        if(s.length()==1&&t.length()==1){
            return s.equals(t)?s:"";
        }

        int size=0;
        int[] charS=new int[60];
        int[] charT=new int[60];

        for(int i=0;i<t.length();i++){

            if(charT[getLocation(t.charAt(i))]++==0){
                size++;
            }

        }

        int slow=0;
        int fast=0;
        String result=s+'#';

        for(;fast<s.length();fast++){

            int locationFast=getLocation(s.charAt(fast));

            if(charT[locationFast]>0&++charS[locationFast]==charT[locationFast]){
                size--;
            }

            while(size==0){

                String temp=s.substring(slow,fast+1);

                result=temp.length()<result.length()?temp:result;

                int locationSlow=getLocation(s.charAt(slow));

                if(charT[locationSlow]>0&charS[locationSlow]--==charT[locationSlow]){
                    size++;
                }

                slow++;

            }

        }

        return result.length()==s.length()+1?"":result;

    }

    public int getLocation(char ch){

        return ('A'<=ch&&ch<='Z')?(ch-'A'):(ch-'a'+26);

    }
}

滑动窗口——O(n+m)

由于 substring 函数操作字符串比较费时，导致同样是滑动窗口，将更新结果值的操作拿到 while 循环外面可以大幅度地优化时间

class Solution {
    public String minWindow(String s, String t) {

        if(s.length()==1&&t.length()==1){
            return s.equals(t)?s:"";
        }

        int size=0;
        int[] charS=new int[60];
        int[] charT=new int[60];

        for(int i=0;i<t.length();i++){

            if(charT[getLocation(t.charAt(i))]++==0){
                size++;
            }

        }

        int slow=0;
        int fast=0;
        String result=s+'#';

        for(;fast<s.length();fast++){

            int locationFast=getLocation(s.charAt(fast));

            if(charT[locationFast]>0&++charS[locationFast]==charT[locationFast]){
                size--;
            }

            int a=-1;
            int b=-1;

            while(size==0){

                a=slow;
                b=fast;

                int locationSlow=getLocation(s.charAt(slow));

                if(charT[locationSlow]>0&charS[locationSlow]--==charT[locationSlow]){
                    size++;
                }

                slow++;

            }

            if(a!=-1&&b!=-1){
                String temp=s.substring(a,b+1);
                result=temp.length()<result.length()?temp:result;
            }

        }

        return result.length()==s.length()+1?"":result;

    }

    public int getLocation(char ch){

        return ('A'<=ch&&ch<='Z')?(ch-'A'):(ch-'a'+26);

    }
}