Added 20 Problems

112-path-sum/112-path-sum.java

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+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    public boolean hasPathSum(TreeNode root, int targetSum) {
+	if(root == null)
+		return false;
+
+	targetSum -= root.val;
+
+	if (targetSum == 0 && root.left == null && root.right == null)
+		return true;
+
+	boolean ans = hasPathSum(root.left, targetSum) || hasPathSum(root.right, targetSum);
+
+	targetSum += root.val;
+
+	return ans;
+}
+}

112-path-sum/README.md

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+<h2><a href="https://leetcode.com/problems/path-sum/">112. Path Sum</a></h2><h3>Easy</h3><hr><div><p>Given the <code>root</code> of a binary tree and an integer <code>targetSum</code>, return <code>true</code> if the tree has a <strong>root-to-leaf</strong> path such that adding up all the values along the path equals <code>targetSum</code>.</p>
+
+<p>A <strong>leaf</strong> is a node with no children.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2021/01/18/pathsum1.jpg" style="width: 500px; height: 356px;">
+<pre><strong>Input:</strong> root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
+<strong>Output:</strong> true
+<strong>Explanation:</strong> The root-to-leaf path with the target sum is shown.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2021/01/18/pathsum2.jpg">
+<pre><strong>Input:</strong> root = [1,2,3], targetSum = 5
+<strong>Output:</strong> false
+<strong>Explanation:</strong> There two root-to-leaf paths in the tree:
+(1 --&gt; 2): The sum is 3.
+(1 --&gt; 3): The sum is 4.
+There is no root-to-leaf path with sum = 5.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre><strong>Input:</strong> root = [], targetSum = 0
+<strong>Output:</strong> false
+<strong>Explanation:</strong> Since the tree is empty, there are no root-to-leaf paths.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li>The number of nodes in the tree is in the range <code>[0, 5000]</code>.</li>
+	<li><code>-1000 &lt;= Node.val &lt;= 1000</code></li>
+	<li><code>-1000 &lt;= targetSum &lt;= 1000</code></li>
+</ul>
+</div>

1155-number-of-dice-rolls-with-target-sum/1155-number-of-dice-rolls-with-target-sum.java

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+class Solution {
+    int mod = 1000000007;
+    public int numRollsToTarget(int n, int k, int target) {
+        int[][] dp = new int[n+1][target+1];
+        for(int i=0;i<dp.length;i++){
+            Arrays.fill(dp[i], -1);
+        }
+        return roll(n, k, target, dp);
+    }
+
+    public int roll(int n, int k, int t, int[][] dp){
+        if(t<0) return 0;
+        if(n==0) 
+            return t==0 ? 1 : 0;
+        if(dp[n][t] ==-1) {
+            int res = 0;
+            for(int i=1;i<=k;i++){
+                res= (res+roll(n-1, k, t-i, dp))%mod;
+            }
+            dp[n][t] = res;
+        }
+        return dp[n][t];
+    }
+}

1155-number-of-dice-rolls-with-target-sum/README.md

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+<h2><a href="https://leetcode.com/problems/number-of-dice-rolls-with-target-sum/">1155. Number of Dice Rolls With Target Sum</a></h2><h3>Medium</h3><hr><div><p>You have <code>n</code> dice and each die has <code>k</code> faces numbered from <code>1</code> to <code>k</code>.</p>
+
+<p>Given three integers <code>n</code>, <code>k</code>, and <code>target</code>, return <em>the number of possible ways (out of the </em><code>k<sup>n</sup></code><em> total ways) </em><em>to roll the dice so the sum of the face-up numbers equals </em><code>target</code>. Since the answer may be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre><strong>Input:</strong> n = 1, k = 6, target = 3
+<strong>Output:</strong> 1
+<strong>Explanation:</strong> You throw one die with 6 faces.
+There is only one way to get a sum of 3.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre><strong>Input:</strong> n = 2, k = 6, target = 7
+<strong>Output:</strong> 6
+<strong>Explanation:</strong> You throw two dice, each with 6 faces.
+There are 6 ways to get a sum of 7: 1+6, 2+5, 3+4, 4+3, 5+2, 6+1.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre><strong>Input:</strong> n = 30, k = 30, target = 500
+<strong>Output:</strong> 222616187
+<strong>Explanation:</strong> The answer must be returned modulo 10<sup>9</sup> + 7.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= n, k &lt;= 30</code></li>
+	<li><code>1 &lt;= target &lt;= 1000</code></li>
+</ul>
+</div>

1202-smallest-string-with-swaps/NOTES.md

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+​

1202-smallest-string-with-swaps/README.md

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+<h2><a href="https://leetcode.com/problems/smallest-string-with-swaps/">1202. Smallest String With Swaps</a></h2><h3>Medium</h3><hr><div><p>You are given a string <code>s</code>, and an array of pairs of indices in the string&nbsp;<code>pairs</code>&nbsp;where&nbsp;<code>pairs[i] =&nbsp;[a, b]</code>&nbsp;indicates 2 indices(0-indexed) of the string.</p>
+
+<p>You can&nbsp;swap the characters at any pair of indices in the given&nbsp;<code>pairs</code>&nbsp;<strong>any number of times</strong>.</p>
+
+<p>Return the&nbsp;lexicographically smallest string that <code>s</code>&nbsp;can be changed to after using the swaps.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre><strong>Input:</strong> s = "dcab", pairs = [[0,3],[1,2]]
+<strong>Output:</strong> "bacd"
+<strong>Explaination:</strong> 
+Swap s[0] and s[3], s = "bcad"
+Swap s[1] and s[2], s = "bacd"
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre><strong>Input:</strong> s = "dcab", pairs = [[0,3],[1,2],[0,2]]
+<strong>Output:</strong> "abcd"
+<strong>Explaination: </strong>
+Swap s[0] and s[3], s = "bcad"
+Swap s[0] and s[2], s = "acbd"
+Swap s[1] and s[2], s = "abcd"</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre><strong>Input:</strong> s = "cba", pairs = [[0,1],[1,2]]
+<strong>Output:</strong> "abc"
+<strong>Explaination: </strong>
+Swap s[0] and s[1], s = "bca"
+Swap s[1] and s[2], s = "bac"
+Swap s[0] and s[1], s = "abc"
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= s.length &lt;= 10^5</code></li>
+	<li><code>0 &lt;= pairs.length &lt;= 10^5</code></li>
+	<li><code>0 &lt;= pairs[i][0], pairs[i][1] &lt;&nbsp;s.length</code></li>
+	<li><code>s</code>&nbsp;only contains lower case English letters.</li>
+</ul>
+</div>

1328-break-a-palindrome/1328-break-a-palindrome.java

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+class Solution {
+    public String breakPalindrome(String palindrome) {
+        int len = palindrome.length();
+        if(len ==1) return "";
+        StringBuilder sb = new StringBuilder(palindrome);
+        //let's traverse the string
+       // System.out.printf("Before:%s\n",sb.toString());
+        int i=0;
+        for( i =0;i<len;i++)
+        {
+            if(sb.toString().charAt(i)!='a'&&len-i-1!=i)
+            { sb.replace(i,i+1,"a");break;}
+
+        }
+        if(i==len)sb.replace(i-1,i,"b");
+      //  System.out.printf("After:%s",sb.toString());
+
+        return sb.toString();
+
+    }
+}

1328-break-a-palindrome/NOTES.md

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+​

1328-break-a-palindrome/README.md

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+<h2><a href="https://leetcode.com/problems/break-a-palindrome/">1328. Break a Palindrome</a></h2><h3>Medium</h3><hr><div><p>Given a palindromic string of lowercase English letters <code>palindrome</code>, replace <strong>exactly one</strong> character with any lowercase English letter so that the resulting string is <strong>not</strong> a palindrome and that it is the <strong>lexicographically smallest</strong> one possible.</p>
+
+<p>Return <em>the resulting string. If there is no way to replace a character to make it not a palindrome, return an <strong>empty string</strong>.</em></p>
+
+<p>A string <code>a</code> is lexicographically smaller than a string <code>b</code> (of the same length) if in the first position where <code>a</code> and <code>b</code> differ, <code>a</code> has a character strictly smaller than the corresponding character in <code>b</code>. For example, <code>"abcc"</code> is lexicographically smaller than <code>"abcd"</code> because the first position they differ is at the fourth character, and <code>'c'</code> is smaller than <code>'d'</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre><strong>Input:</strong> palindrome = "abccba"
+<strong>Output:</strong> "aaccba"
+<strong>Explanation:</strong> There are many ways to make "abccba" not a palindrome, such as "<u>z</u>bccba", "a<u>a</u>ccba", and "ab<u>a</u>cba".
+Of all the ways, "aaccba" is the lexicographically smallest.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre><strong>Input:</strong> palindrome = "a"
+<strong>Output:</strong> ""
+<strong>Explanation:</strong> There is no way to replace a single character to make "a" not a palindrome, so return an empty string.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= palindrome.length &lt;= 1000</code></li>
+	<li><code>palindrome</code> consists of only lowercase English letters.</li>
+</ul>
+</div>

1342-number-of-steps-to-reduce-a-number-to-zero/1342-number-of-steps-to-reduce-a-number-to-zero.java

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+class Solution {
+    public int numberOfSteps(int num) {
+        return count(num,0); 
+    }
+    public int count(int num, int steps){
+        if(num==0) return steps;
+        if(num==1) return steps+1;
+
+        if(num%2==0){
+            steps++;
+            return count((num/2), steps);
+        }else{
+            steps++;
+           return count((num-1), steps);
+        }
+    }
+}

1342-number-of-steps-to-reduce-a-number-to-zero/NOTES.md

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+​

1342-number-of-steps-to-reduce-a-number-to-zero/README.md

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+<h2><a href="https://leetcode.com/problems/number-of-steps-to-reduce-a-number-to-zero/">1342. Number of Steps to Reduce a Number to Zero</a></h2><h3>Easy</h3><hr><div><p>Given an integer <code>num</code>, return <em>the number of steps to reduce it to zero</em>.</p>
+
+<p>In one step, if the current number is even, you have to divide it by <code>2</code>, otherwise, you have to subtract <code>1</code> from it.</p>
+
+<p>&nbsp;</p>
+<p><strong>Example 1:</strong></p>
+
+<pre><strong>Input:</strong> num = 14
+<strong>Output:</strong> 6
+<strong>Explanation:</strong>&nbsp;
+Step 1) 14 is even; divide by 2 and obtain 7.&nbsp;
+Step 2) 7 is odd; subtract 1 and obtain 6.
+Step 3) 6 is even; divide by 2 and obtain 3.&nbsp;
+Step 4) 3 is odd; subtract 1 and obtain 2.&nbsp;
+Step 5) 2 is even; divide by 2 and obtain 1.&nbsp;
+Step 6) 1 is odd; subtract 1 and obtain 0.
+</pre>
+
+<p><strong>Example 2:</strong></p>
+
+<pre><strong>Input:</strong> num = 8
+<strong>Output:</strong> 4
+<strong>Explanation:</strong>&nbsp;
+Step 1) 8 is even; divide by 2 and obtain 4.&nbsp;
+Step 2) 4 is even; divide by 2 and obtain 2.&nbsp;
+Step 3) 2 is even; divide by 2 and obtain 1.&nbsp;
+Step 4) 1 is odd; subtract 1 and obtain 0.
+</pre>
+
+<p><strong>Example 3:</strong></p>
+
+<pre><strong>Input:</strong> num = 123
+<strong>Output:</strong> 12
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>0 &lt;= num &lt;= 10<sup>6</sup></code></li>
+</ul>
+</div>

1578-minimum-time-to-make-rope-colorful/1578-minimum-time-to-make-rope-colorful.java

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+class Solution {
+    public int minCost(String colors, int[] neededTime) {
+      int groupSum=0;
+      int maxSum=0;
+      int res=0;
+
+      for(int i=0;i<colors.length();i++){
+        if(i>0 &&colors.charAt(i)!=colors.charAt(i-1)){
+         res+=groupSum-maxSum;
+          groupSum=0;
+           maxSum=0;
+         }
+
+         groupSum+=neededTime[i];
+        maxSum=Math.max(maxSum,neededTime[i]);
+            }
+            res+=groupSum-maxSum;
+      return res;      
+    }
+}

1578-minimum-time-to-make-rope-colorful/NOTES.md

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+​