Merge pull request #27 from colorbox/349

349. Intersection of Two Arrays

Author: colorbox

349/step1.cpp

@@ -0,0 +1,40 @@
+/*
+Time: 8:40
+
+Time: O(N log N + M log M)
+Space: O(N + M)
+
+nums1.size() == N
+nums2.size() == M 
+*/
+class Solution {
+public:
+  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
+    set<int> nums1_set;
+    for (int num : nums1) {
+      if (nums1_set.find(num) != nums1_set.end()) {
+        continue;
+      }
+      nums1_set.insert(num);
+    }
+    set<int> intersection;
+    for (int num : nums2) {
+      if (nums1_set.find(num) == nums1_set.end()) {
+        continue;
+      }
+      if (intersection.find(num) != intersection.end()) {
+        continue;
+      }
+      if (nums1_set.find(num) != nums1_set.end()) {
+        intersection.insert(num);
+      }
+    }
+
+    vector<int> answer;
+    for (int num : intersection) {
+      answer.emplace_back(num);
+    }
+
+    return answer;
+  }
+};

349/step2_1.cpp

@@ -0,0 +1,31 @@
+/*
+mapで書き直したパターン
+単一のmapでカウントできるのでsetを利用するstep1よりもシンプルになった
+Time: O(N + M)
+Space: 
+*/
+class Solution {
+public:
+  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
+    map<int, int> nums_count;
+    for (int num : nums1) {
+      if (nums_count[num] == 1) {
+        continue;
+      }
+      nums_count[num]++;
+    }
+    for (int num : nums2) {
+      if (nums_count[num] != 1) {
+        continue;
+      }
+      nums_count[num]++;
+    }
+    vector<int> intersected_nums;
+    for (auto [num, count] : nums_count) {
+      if (count == 2) {
+        intersected_nums.push_back(num);
+      }
+    }
+    return intersected_nums;
+  }
+};

349/step2_1_fix.cpp

@@ -0,0 +1,17 @@
+class Solution {
+public:
+  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
+    map<int, int> num_to_count;
+    for (int num : nums1) {
+      num_to_count[num]++;
+    }
+    vector<int> intersected_nums;
+    for(int num : nums2) {
+      if (num_to_count[num] > 0) {
+        intersected_nums.push_back(num);
+        num_to_count[num] = 0;
+      }
+    }
+    return intersected_nums;
+  }
+};

349/step2_2.cpp

@@ -0,0 +1,33 @@
+/*
+Time: O(N log N + M log M)
+Space: O(N + M)
+
+nums1.size() == N
+nums2.size() == M 
+
+２つのnumsをソートしてマージソートっぽくする手法
+https://github.com/gcc-mirror/gcc/blob/8762bb1b004c442b8dbb22a6d9eb0b7da4a3e59f/libstdc%2B%2B-v3/include/bits/stl_algo.h#L5208-L5230
+*/
+class Solution {
+public:
+  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
+    sort(nums1.begin(), nums1.end());
+    sort(nums2.begin(), nums2.end());
+    vector<int> intersected_nums;
+    int i = 0, j = 0;
+    while (i < nums1.size() && j < nums2.size()) {
+      if (nums1[i] < nums2[j]) {
+        i++;
+      } else if (nums2[j] < nums1[i]) {
+        j++;
+      } else {
+        if (intersected_nums.empty() || intersected_nums.back() != nums1[i]) {
+          intersected_nums.push_back(nums1[i]);
+        }
+        i++;
+        j++;
+      }
+    }
+    return intersected_nums;
+  }
+};

349/step2_3.cpp

@@ -0,0 +1,21 @@
+/*
+`std::set_intersection`を使うパターン
+
+Time : O(N log N + M log M)
+Space: O(N + M)
+
+nums1.size() == N
+nums2.size() == M 
+*/
+class Solution {
+public:
+  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
+    sort(nums1.begin(), nums1.end());
+    sort(nums2.begin(), nums2.end());
+    vector<int> intersected_nums;
+    set_intersection(nums1.begin(), nums1.end(), nums2.begin(), nums2.end(), inserter(intersected_nums, intersected_nums.end()));
+    auto it = unique(intersected_nums.begin(), intersected_nums.end());
+    intersected_nums.erase(it, intersected_nums.end());
+    return intersected_nums;
+  }
+};

349/step2_3_fix.cpp

@@ -0,0 +1,10 @@
+class Solution {
+public:
+  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
+    set<int> set1(nums1.begin(), nums1.end());
+    set<int> set2(nums2.begin(), nums2.end());
+    vector<int> intersected_nums;
+    std::set_intersection(set1.begin(), set1.end(), set2.begin(), set2.end(), std::inserter(intersected_nums, intersected_nums.end()));
+    return intersected_nums;
+  }
+};

349/step3.cpp

@@ -0,0 +1,17 @@
+class Solution {
+public:
+  vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
+    set<int> unique_nums;
+    for (int num : nums1) {
+      unique_nums.insert(num);
+    }
+    vector<int> intersected_nums;
+    for (int num : nums2) {
+      if (unique_nums.contains(num)) {
+        intersected_nums.push_back(num);
+        unique_nums.erase(num);
+      }
+    }
+    return intersected_nums;
+  }
+};