Add solutions for new topics

Author: kiranpalsingh1806

solutions/bellman-ford.md

@@ -0,0 +1,63 @@
+# Bellman Ford Algorithm
+
+## Cheapest Flights Within K Stops
+
+```cpp
+class Solution {
+public:
+    int findCheapestPrice(int n, vector<vector<int>>& flights, int src, int dst, int k) {
+        vector<int> dist(n, 1e9);
+        
+        dist[src] = 0; 
+        
+        // K relaxation
+        
+        for(int i = 0; i <= k; i++) {
+            auto temp = dist;
+            
+            for(auto &e : flights) {
+                int u = e[0], v = e[1], w = e[2];
+                
+                dist[v] = min(dist[v], temp[u] + w);
+            }
+        }
+        
+        if(dist[dst] == 1e9) {
+            return -1;
+        } else {
+            return dist[dst];
+        }
+    }
+};
+```
+
+## Network Delay Time
+
+```cpp
+class Solution {
+public:
+    int networkDelayTime(vector<vector<int>>& times, int n, int k) {
+        vector<int> dist(n, 1e9);
+        
+        dist[k - 1] = 0;
+        
+        for(int i = 0; i < n; i++) {
+            
+            for(auto &e : times) {
+                int u = e[0] - 1, v = e[1] - 1, w = e[2];
+                if(dist[u] != 1e9) {
+                    dist[v] = min(dist[v], dist[u] + w);
+                }   
+            }
+        }
+        
+        int answer = *max_element(dist.begin(), dist.end());
+        
+        if(answer == 1e9) {
+            return -1;
+        } else {
+            return answer;
+        }
+    }
+};
+```

solutions/custom-comparator.md

@@ -0,0 +1,35 @@
+# Custom Comparator
+
+## Sort Array By Parity
+
+```cpp
+vector<int> sortArrayByParity(vector<int>& nums) {
+    sort(nums.begin(), nums.end(), [&](int a, int b) {
+        return (a % 2) < (b % 2); 
+    });
+    
+    return nums;
+}
+```
+
+## Sort The People
+
+```cpp
+vector<string> sortPeople(vector<string>& names, vector<int>& heights) { 
+    int N = names.size();
+    vector<int> idx(N, 0);
+    iota(idx.begin(), idx.end(), 0);
+    
+    sort(idx.begin(), idx.end(), [&](auto &i, auto &j) {
+        return heights[i] > heights[j]; 
+    });
+    
+    vector<string> ans;
+    
+    for (auto &a : idx) {
+        ans.push_back(names[a]);
+    }
+    
+    return ans;
+}
+```

solutions/segment-tree.md

@@ -1,10 +1,13 @@
-- [Sum of Even Numbers After Queries](#sum-of-even-numbers-after-queries)
-- [Range Sum Query Mutable](#range-sum-query-mutable)
-- [Longest Increasing Subsequence - II](#longest-increasing-subsequence---ii)
-- [Shifting Letters - II](#shifting-letters---ii)
-- [Falling Squares](#falling-squares)
+# Segment Tree
 
-# Sum of Even Numbers After Queries
+- [Segment Tree](#segment-tree)
+  - [Sum of Even Numbers After Queries](#sum-of-even-numbers-after-queries)
+  - [Range Sum Query Mutable](#range-sum-query-mutable)
+  - [Longest Increasing Subsequence - II](#longest-increasing-subsequence---ii)
+  - [Shifting Letters - II](#shifting-letters---ii)
+  - [Falling Squares](#falling-squares)
+
+## Sum of Even Numbers After Queries
 
 ```cpp
 struct segtree {
@@ -64,7 +67,7 @@ public:
 };
 ```
 
-# Range Sum Query Mutable
+## Range Sum Query Mutable
 
 ```cpp
 struct segtree {
@@ -134,7 +137,7 @@ private:
 };
 ```
 
-# Longest Increasing Subsequence - II
+## Longest Increasing Subsequence - II
 
 ```cpp
 struct segtree {
@@ -191,7 +194,7 @@ public:
 };
 ```
 
-# Shifting Letters - II
+## Shifting Letters - II
 
 ```cpp
 class Solution {
@@ -247,7 +250,7 @@ public:
 };
 ```
 
-# Falling Squares
+## Falling Squares
 
 ```cpp
 class Solution {