Added new solutions

leetcode/leetcode/0001-two-sum/0001-two-sum.cpp

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+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        for(int i=0;i<nums.size()-1;i++){
+            for(int j=i+1;j<nums.size();j++){
+                if(nums[i]+nums[j]==target){
+                    return{i,j};
+                }
+            }
+        }
+        return {};
+
+    }
+};

leetcode/leetcode/0001-two-sum/0001-two-sum.java

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+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        HashMap<Integer,Integer> map = new HashMap<>();
+
+        int[] ans = {-1,-1};
+
+        for(int i = 0;i<nums.length;i++){
+            if(map.containsKey(target-nums[i])){
+                ans[0] = i;
+                ans[1] = map.get(target-nums[i]);
+                return ans;
+            }
+            map.put(nums[i],i);
+        }
+        return ans;
+    }
+}

leetcode/leetcode/0001-two-sum/NOTES.md

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+​

leetcode/leetcode/0001-two-sum/README.md

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+<h2><a href="https://leetcode.com/problems/two-sum">1. Two Sum</a></h2><h3>Easy</h3><hr><p>Given an array of integers <code>nums</code>&nbsp;and an integer <code>target</code>, return <em>indices of the two numbers such that they add up to <code>target</code></em>.</p>
+
+<p>You may assume that each input would have <strong><em>exactly</em> one solution</strong>, and you may not use the <em>same</em> element twice.</p>
+
+<p>You can return the answer in any order.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [2,7,11,15], target = 9
+<strong>Output:</strong> [0,1]
+<strong>Explanation:</strong> Because nums[0] + nums[1] == 9, we return [0, 1].
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [3,2,4], target = 6
+<strong>Output:</strong> [1,2]
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [3,3], target = 6
+<strong>Output:</strong> [0,1]
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>2 &lt;= nums.length &lt;= 10<sup>4</sup></code></li>
+	<li><code>-10<sup>9</sup> &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
+	<li><code>-10<sup>9</sup> &lt;= target &lt;= 10<sup>9</sup></code></li>
+	<li><strong>Only one valid answer exists.</strong></li>
+</ul>
+
+<p>&nbsp;</p>
+<strong>Follow-up:&nbsp;</strong>Can you come up with an algorithm that is less than <code>O(n<sup>2</sup>)</code><font face="monospace">&nbsp;</font>time complexity?

leetcode/leetcode/0003-longest-substring-without-repeating-characters/0003-longest-substring-without-repeating-characters.java

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+class Solution {
+    public int lengthOfLongestSubstring(String s) {
+        boolean[] freq = new boolean[256];
+        int start = 0;
+        int end = 0;
+        int max = 0;
+        while(end<s.length()){
+            if(freq[(int) s.charAt(end)]){
+                freq[(int) s.charAt(start)] = false;
+                start++;
+            }
+            else{
+                freq[(int) s.charAt(end)] = true;
+                end++; 
+            }
+            max = Math.max(max,end-start);
+        }
+        return max;
+    }
+}

leetcode/leetcode/0003-longest-substring-without-repeating-characters/README.md

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+<h2><a href="https://leetcode.com/problems/longest-substring-without-repeating-characters">3. Longest Substring Without Repeating Characters</a></h2><h3>Medium</h3><hr><p>Given a string <code>s</code>, find the length of the <strong>longest</strong> <span data-keyword="substring-nonempty"><strong>substring</strong></span> without duplicate characters.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;abcabcbb&quot;
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The answer is &quot;abc&quot;, with the length of 3.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;bbbbb&quot;
+<strong>Output:</strong> 1
+<strong>Explanation:</strong> The answer is &quot;b&quot;, with the length of 1.
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;pwwkew&quot;
+<strong>Output:</strong> 3
+<strong>Explanation:</strong> The answer is &quot;wke&quot;, with the length of 3.
+Notice that the answer must be a substring, &quot;pwke&quot; is a subsequence and not a substring.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>0 &lt;= s.length &lt;= 5 * 10<sup>4</sup></code></li>
+	<li><code>s</code> consists of English letters, digits, symbols and spaces.</li>
+</ul>

leetcode/leetcode/0005-longest-palindromic-substring/0005-longest-palindromic-substring.java

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+class Solution {
+    public String longestPalindrome(String s) {
+        int n = s.length();
+        boolean[][] dp = new boolean[n][n];
+        int[] ans = new int[]{0, 0};
+
+        for (int i = 0; i < n; i++) {
+            dp[i][i] = true;
+        }
+
+        for (int i = 0; i < n - 1; i++) {
+            if (s.charAt(i) == s.charAt(i + 1)) {
+                dp[i][i + 1] = true;
+                ans[0] = i;
+                ans[1] = i + 1;
+            }
+        }
+
+        for (int diff = 2; diff < n; diff++) {
+            for (int i = 0; i < n - diff; i++) {
+                int j = i + diff;
+                if (s.charAt(i) == s.charAt(j) && dp[i + 1][j - 1]) {
+                    dp[i][j] = true;
+                    ans[0] = i;
+                    ans[1] = j;
+                }
+            }
+        }
+
+        int i = ans[0];
+        int j = ans[1];
+        return s.substring(i, j + 1);
+    }
+}

leetcode/leetcode/0005-longest-palindromic-substring/NOTES.md

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+​

leetcode/leetcode/0005-longest-palindromic-substring/README.md

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+<h2><a href="https://leetcode.com/problems/longest-palindromic-substring/">5. Longest Palindromic Substring</a></h2><h3>Medium</h3><hr><div><p>Given a string <code>s</code>, return <em>the longest</em> <span data-keyword="palindromic-string"><em>palindromic</em></span> <span data-keyword="substring-nonempty"><em>substring</em></span> in <code>s</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre><strong>Input:</strong> s = "babad"
+<strong>Output:</strong> "bab"
+<strong>Explanation:</strong> "aba" is also a valid answer.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre><strong>Input:</strong> s = "cbbd"
+<strong>Output:</strong> "bb"
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
+	<li><code>s</code> consist of only digits and English letters.</li>
+</ul>
+</div>

leetcode/leetcode/0009-palindrome-number/0009-palindrome-number.java

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+class Solution {
+    public boolean check(ArrayList<Integer> list){
+        int low = 0;
+        int high = list.size()-1;
+        while(low<high){
+            if(list.get(low) != list.get(high)){
+                return false;
+            }
+            low++;
+            high--;
+        }
+        return true;
+    }
+    public boolean isPalindrome(int x) {
+        if(x<0) return false;
+        ArrayList<Integer> list = new ArrayList<>();
+        while(x!=0){
+            list.add(x%10);
+            x = x/10;
+        }
+        return check(list);
+    }
+}

leetcode/leetcode/0009-palindrome-number/NOTES.md

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+​

leetcode/leetcode/0011-container-with-most-water/0011-container-with-most-water.java

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+class Solution {
+    public int maxArea(int[] height) {
+
+        // Initilization the two pointer 
+        int low  = 0;
+        int high = height.length -1;
+
+        int ans = Integer.MIN_VALUE;
+        while(low<high){
+            // finding the min height for the water level
+            int currHeight = Math.min(height[low],height[high]); 
+
+            // finding the width
+            int width  = high-low;
+
+            // calculating the area and updating the maximum area
+            ans = Math.max(ans,currHeight*width);
+
+            // Changing the pointer which has minimum height
+            if(height[low]>height[high]){
+                high--;
+            } else{
+                low++;
+            }
+        }
+        return ans;
+    }
+}

leetcode/leetcode/0011-container-with-most-water/NOTES.md

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+​

leetcode/leetcode/0011-container-with-most-water/README.md

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+<h2><a href="https://leetcode.com/problems/container-with-most-water">11. Container With Most Water</a></h2><h3>Medium</h3><hr><p>You are given an integer array <code>height</code> of length <code>n</code>. There are <code>n</code> vertical lines drawn such that the two endpoints of the <code>i<sup>th</sup></code> line are <code>(i, 0)</code> and <code>(i, height[i])</code>.</p>
+
+<p>Find two lines that together with the x-axis form a container, such that the container contains the most water.</p>
+
+<p>Return <em>the maximum amount of water a container can store</em>.</p>
+
+<p><strong>Notice</strong> that you may not slant the container.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+<img alt="" src="https://s3-lc-upload.s3.amazonaws.com/uploads/2018/07/17/question_11.jpg" style="width: 600px; height: 287px;" />
+<pre>
+<strong>Input:</strong> height = [1,8,6,2,5,4,8,3,7]
+<strong>Output:</strong> 49
+<strong>Explanation:</strong> The above vertical lines are represented by array [1,8,6,2,5,4,8,3,7]. In this case, the max area of water (blue section) the container can contain is 49.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> height = [1,1]
+<strong>Output:</strong> 1
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>n == height.length</code></li>
+	<li><code>2 &lt;= n &lt;= 10<sup>5</sup></code></li>
+	<li><code>0 &lt;= height[i] &lt;= 10<sup>4</sup></code></li>
+</ul>

leetcode/leetcode/0013-roman-to-integer/0013-roman-to-integer.java

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+class Solution {
+    public int romanToInt(String s) {
+        int ans = 0;
+        int index = 0;
+
+        while(index<s.length()){
+            char c = s.charAt(index);
+            if(c == 'I'){
+                if(index+1<s.length()){
+                    if(s.charAt(index+1) == 'V'){
+                        ans+=4;
+                        index+=2;
+                    }else if(s.charAt(index+1) == 'X'){
+                        ans+=9;
+                        index+=2;
+                    }else {
+                        ans+=1;
+                        index+=1;
+                    }
+                }else{
+                    ans+=1;
+                    index+=1;
+                }
+            }else if(c== 'V'){
+                ans+=5;
+                index++;
+
+            }else if(c == 'X'){
+                if(index+1<s.length()){
+                    if(s.charAt(index+1) == 'L'){
+                        ans+=40;
+                        index+=2;
+                    }else if(s.charAt(index+1) == 'C'){
+                        ans+=90;
+                        index+=2;
+                    }else {
+                        ans+=10;
+                        index+=1;
+                    }
+                }else{
+                    ans+=10;
+                    index+=1;
+                }
+
+            }else if(c == 'L'){
+                ans+=50;
+                index++;
+
+            }else if(c == 'C'){
+                if(index+1<s.length()){
+                    if(s.charAt(index+1) == 'D'){
+                        ans+=400;
+                        index+=2;
+                    }else if(s.charAt(index+1) == 'M'){
+                        ans+=900;
+                        index+=2;
+                    }else {
+                        ans+=100;
+                        index+=1;
+                    }
+                }else{
+                    ans+=100;
+                    index+=1;
+                }
+
+            }else if(c == 'D'){
+                ans+=500;
+                index++;
+
+            }else if(c == 'M'){
+                ans+=1000;
+                index++;
+            }
+        }
+        return ans;
+    }
+}

leetcode/leetcode/0013-roman-to-integer/NOTES.md

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+​