Sep16: min distance, math hashset, sliding window [M]

traverse, no algorithm needed, O(N).

hashset find time: O(logN), Space: O(N), overall: O(N).

Sliding window problem: O(N), Space: O(1)

Author: aucker

daily/Sep16.cc

@@ -0,0 +1,97 @@
+#include <set>
+using namespace std;
+
+class Solution {
+ public:
+  /**
+   * @brief LC: return min distance from start to destination [E]
+   * there is only 2 ways to go from start to destination
+   * Time: O(N), Space: O(1)
+   *
+   * @param distance
+   * @param start
+   * @param destination
+   * @return int
+   */
+  int distanceBetweenBusStop(vector<int>& distance, int start,
+                             int destination) {
+    int sum = 0;
+    for (int ele : distance) {
+      sum += ele;
+    }
+    int ans = 0;
+    if (start < destination) {
+      for (int i = start; i < destination; i++) {
+        ans += distance[i];
+      }
+    } else if (start > destination) {
+      for (int i = destination; i < start; i++) {
+        ans += distance[i];
+      }
+    } else {
+      return 0;
+    }
+    return ans < (sum - ans) ? ans : (sum - ans);
+  }
+
+  /**
+   * @brief Sum swap [M]
+   * Pure math, use hashset to store the temp arr
+   * Time: O(N), Space: O(N), find for set is O(logN)
+   *
+   * @param array1
+   * @param array2
+   * @return vector<int>
+   */
+  vector<int> findSwapValue(vector<int>& array1, vector<int>& array2) {
+    int sum1 = 0, sum2 = 0;
+    set<int> hashset;
+    for (int arr : array1) {
+      sum1 += arr;
+    }
+    for (int arr : array2) {
+      sum2 += arr;
+      hashset.insert(arr);
+    }
+
+    int diff = sum1 - sum2;
+    if (diff % 2 != 0) {
+      return {};
+    }
+    diff /= 2;
+
+    vector<int> ans(2, 0);
+    for (int ele : array1) {
+      if (hashset.find(ele - diff) != hashset.end()) {
+        ans[0] = ele;
+        ans[1] = ele - diff;
+        return ans;
+      }
+    }
+    return {};
+  }
+
+  /**
+   * @brief LC1180: Sliding window [E]
+   * Mind the edge of window, Time: O(N) Space: O(1)
+   *
+   * @param s
+   * @return int
+   */
+  int countLetters(string s) {
+    int len = s.length();
+    int le = 0, ri = le;
+    int ans = 0;
+
+    while (le < len && le <= ri) {
+      if (s[ri] == s[le]) {
+        ans++;
+        ri++;
+      } else {
+        le++;
+        ri = le;
+      }
+    }
+    return ans;
+  }
+};