刷题记录帖

394. Decode String
done

Find the bug of the following code
class Solution {
    public String decodeString(String s) {
        StringBuilder ans = new StringBuilder();
        Stack<Character> stack = new Stack<>();
        Character[] ch = s.toCharArray();        for(int i=0; i<ch.length; i++){
            Character c = ch;
            if(Character.isDigit(c)||c=='['||Character.isLetter(c)){
                stack.push(c);
            }else{
                StringBuilder helper = new StringBuilder();
                while(stack.peek()!='['){
                    helper.append(stack.pop());
                }
                stack.pop();
                StringBuilder helper1= new StringBuilder();
                StringBuilder num = new StringBuilder();
                while(!stack.isEmpty()&&Character.isDigit(stack.peek())){   
                    num.append(stack.pop());
                }
                 int tag =Integer.parseInt(num.reverse().toString());
                while(tag!=0){
                    helper1.append(helper.toString());
                    tag--;
                }
                String decode = helper1.toString();
                Char[] ch1= decode.toCharArray();
                for(int j=ch1.length-1; j>=0;j--){
                    stack.push(ch1[j]);
                }
            }
        }
        while(!stack.isEmpty()){
            ans.append(Stack.pop());
        }
        return ans.reverse().toString();
    }
}
Study another method.
And compare the idea.
Summary for string and character.
150. Evaluate Reverse Polish Notation

150. Evaluate Reverse Polish Notation
done
227. Basic Calculator II
another one I dont understand.
224. Basic Calculator

227. Basic Calculator II
done
224. Basic Calculator

739. Daily Temperatures

CONTEST
Check If It Is a Straight Line

when using / pay attention:
substract 0
a/b*c    和a÷b乘c are different

习惯养成：
不管是什么样的code， 每一次提交之前都要沉住气，检查，至少心里想一个test case，检查基本错误。

前期可能很慢，但是习惯养成之后就会越来越好。

739. Daily Temperatures
done

Summary of stack
682. Baseball Game
496. Next Greater Element I
844. Backspace String Compare
Integer.valueOf
java.lang.Integer.valueOf(String str) is an inbuilt method which is used to return an Integer object, holding the value of the specified String str.
效率极低， 要怎么办呢？

What is Binary Search?
why time complexity is O(logn).
https://www.geeksforgeeks.org/co ... s-of-binary-search/
https://www.youtube.com/watch?v=v57lNF2mb_s
69. Sqrt(x)
278. First Bad Version
875. Koko Eating Bananas
378. Kth Smallest Element in a Sorted Matrix

What is Binary Search?
https://www.geeksforgeeks.org/binary-search/
875. Koko Eating Bananas
int b= a/k;
time+ =a==b*k? b: b+1;
[30,11,23,4,0]
5
why？
287. Find the Duplicate Number
378. Kth Smallest Element in a Sorted Matrix
https://leetcode.com/problems/kt ... and-Clean-Java-Code
350. Intersection of Two Arrays II

981. Time Based Key-Value Store
392. Is Subsequence
why binary search?
704. Binary Search
done
240. Search a 2D Matrix II
why？

162. Find Peak Element
121. Best Time to Buy and Sell Stock
122. Best Time to Buy and Sell Stock II
123. Best Time to Buy and Sell Stock III

zhouwu
528. Random Pick with Weight

today mock interview
想一想 min stack 这个题目怎么讲
374. Guess Number Higher or Lower