added three new algos

longest_substr_without_repeating_chars.cpp

@@ -0,0 +1,16 @@
+#include <iostream>
+#include <unordered_set>
+using namespace std;
+
+int lengthOfLongestSubstring(string s) {
+    unordered_set<char> seen;
+    int maxLen = 0, left = 0;
+    for (int right = 0; right < s.size(); right++) {
+        while (seen.find(s[right]) != seen.end()) {
+            seen.erase(s[left++]);
+        }
+        seen.insert(s[right]);
+        maxLen = max(maxLen, right - left);
+    }
+    return maxLen;
+}

merge_intervals.cpp

@@ -0,0 +1,17 @@
+#include <iostream>
+#include <vector>
+#include <algorithm>
+using namespace std;
+
+vector<vector<int>> merge(vector<vector<int>>& intervals) {
+    sort(intervals.begin(), intervals.end());
+    vector<vector<int>> merged;
+    for (auto interval : intervals) {
+        if (merged.empty() || merged.back()[1] < interval[1]) {
+            merged.push_back(interval);
+        } else {
+            merged.back()[1] = max(merged.back()[1], interval[1]);
+        }
+    }
+    return merged;
+}

peak_element.cpp

@@ -0,0 +1,15 @@
+#include <iostream>
+#include <vector>
+using namespace std;
+
+int findPeakElement(vector<int>& nums) {
+    int left = 0, right = nums.size();
+    while (left < right) {
+        int mid = left + (right - left) / 2;
+        if (nums[mid] > nums[mid + 1])
+            right = mid;
+        else
+            left = mid + 1;
+    }
+    return left;
+}