Problem 1: Contains Duplicate

Link to the problem: https://leetcode.com/problems/contains-duplicate/

class Solution {
    public boolean containsDuplicate(int[] nums) {
        Map<Integer, Integer> map = new HashMap<>();
        for(int i:nums){
            if(map.containsKey(i))
                return true;
            map.put(i, 1);
        }
        return false;
    }
}

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Problem 2: Move Zeroes

Link to the problem: https://leetcode.com/problems/move-zeroes/

class Solution {
    public void moveZeroes(int[] nums) {
        List<Integer> list = new ArrayList<>();
        for(int i=0; i<nums.length; i++){
            if(nums[i]==0)
                list.add(i);
            else{
                if(list.isEmpty())
                    continue;
                else{
                    int temp = nums[i];
                    nums[i--] = nums[list.get(0)];
                    nums[list.get(0)] = temp;
                    list.remove(0);
                }
            }
        }
    }
}

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Problem 3: Squares of a sorted array

Link to the problem: https://leetcode.com/problems/squares-of-a-sorted-array/

class Solution {
    public int[] sortedSquares(int[] nums) {
        for(int i=0; i<nums.length; i++)
            nums[i] *= nums[i];
        Arrays.sort(nums);
        return nums;
    }
}

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Problem 4: First Bad Version

Link to the problem: https://leetcode.com/problems/first-bad-version/

/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int low=0;
        if(isBadVersion(1))
            return 1;
        while(low<n){
            int mid = low+(n-low)/2;
            if(isBadVersion(low)){
                if(!isBadVersion(low-1))
                    return low;
            }else if(isBadVersion(n)){
                if(!isBadVersion(n-1))
                    return n;
            }
            if(isBadVersion(mid)){
                if(!isBadVersion(mid-1))
                    return mid;
                n=mid;
            }else{
                low=mid+1;
            }
        }
        return -1;
    }
}

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Problem 5: Backspace String Compare

Link to the problem: https://leetcode.com/problems/backspace-string-compare/

class Solution {
    public boolean backspaceCompare(String s, String t) {
        Stack<Character> stack = new Stack<>();
        for(char ch:s.toCharArray()){
            if(ch!='#')
                stack.push(ch);
            else if(!stack.isEmpty())
                stack.pop();
        }
        s = stack.toString();
        stack.clear();
        for(char ch:t.toCharArray()){
            if(ch!='#')
                stack.push(ch);
            else if(!stack.isEmpty())
                stack.pop();
        }
        t = stack.toString();
        return s.equals(t)?true:false;
    }
}

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