some leetcode problems

Author: naowalrahman

.clang-format

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 ---
 BasedOnStyle: Chromium
 IndentWidth: 4
+ColumnLimit: 200

leetcode/1415.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+   public:
+    string ans;
+    int i = 0, n, k;
+
+    void helper(string s) {
+        if (s.size() == n) {
+            if (i == k)
+                return;
+            ans = s;
+            ++i;
+            return;
+        }
+        if (s.empty()) {
+            helper(s + 'a');
+            helper(s + 'b');
+            helper(s + 'c');
+        } else {
+            char c1, c2;
+            int last = s.size() - 1;
+            if (s[last] == 'a')
+                c1 = 'b', c2 = 'c';
+            else if (s[last] == 'b')
+                c1 = 'a', c2 = 'c';
+            else
+                c1 = 'a', c2 = 'b';
+
+            helper(s + c1);
+            helper(s + c2);
+        }
+    }
+    string getHappyString(int n, int k) {
+        this->n = n;
+        this->k = k;
+        helper("");
+        if (k > i)
+            return "";
+        return ans;
+    }
+};

leetcode/2349.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+class NumberContainers {
+   public:
+    map<int, set<int>> num_to_indexes;
+    map<int, int> index_to_num;
+    NumberContainers() {
+        /*
+         map<int, set<int>>, key = number, val = index
+         map<int, int>, key = index, val = number
+        */
+    }
+
+    void change(int index, int number) {
+        if (index_to_num[index] == 0) {
+            index_to_num[index] = number;
+            if (num_to_indexes.find(number) == num_to_indexes.end()) {
+                num_to_indexes[number] = set<int>({index});
+            } else {
+                num_to_indexes[number].insert(index);
+            }
+        } else {
+            int prev = index_to_num[index];
+            num_to_indexes[prev].erase(num_to_indexes[prev].find(index));
+            index_to_num[index] = number;
+            num_to_indexes[number].insert(index);
+        }
+    }
+
+    int find(int number) {
+        int get = *(num_to_indexes[number].begin());
+        return get == 0 ? -1 : get;
+    }
+};

leetcode/2516.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+   public:
+    int takeCharacters(string s, int k) {
+        // pick an index to be a set number of right minutes, get the char count by doing suffix subtraction for a, b, c.
+        // binary search the prefix sums for a, b, c to get corresponding left minutes indicies, take the max of that.
+        // take the max over all possible right minute indexes [0, n - 1]
+        // runs in O(n lg n)
+        int n = s.size();
+        vector<vector<int>> pfx(3, vector<int>(n + 1)), sfx(3, vector<int>(n + 1));
+        for (int i = 0; i < 3; i++) {
+            for (int j = 1; j <= n; j++) {
+                pfx[i][j] = pfx[i][j - 1] + (s[j - 1] - 'a' == i);
+            }
+        }
+        for (int i = 0; i < 3; i++) {
+            for (int j = n - 1; j >= 0; j--) {
+                sfx[i][j] = sfx[i][j + 1] + (s[j] - 'a' == i);
+            }
+        }
+
+        int ans = INT_MAX;
+        vector<int> L(3);
+        for (int r = 0; r <= n; r++) {
+            for (int i = 0; i < 3; i++) {
+                L[i] = lower_bound(pfx[i].begin(), pfx[i].end(), k - sfx[i][r]) - pfx[i].begin();
+            }
+            ans = min(ans, *max_element(L.begin(), L.end()) + n - r);
+        }
+
+        return ans <= n ? ans : -1;
+    }
+};

leetcode/2563.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+   public:
+    long long countFairPairs(vector<int>& nums, int lower, int upper) {
+        long long n = nums.size(), ans = 0;
+        sort(nums.begin(), nums.end());
+        for (int i = 0; i < n; i++) {
+            auto j = upper_bound(nums.begin() + i + 1, nums.end(), upper - nums[i]);
+            auto k = lower_bound(nums.begin() + i + 1, nums.end(), lower - nums[i]);
+            ans += j - k;
+        }
+        return ans;
+    }
+};