Add 015 cpp solution

solution/015.3Sum/solution.cpp

@@ -0,0 +1,89 @@
+class Solution {
+public:
+     vector<vector<int> > threeSum(vector<int> &num) {
+        return threeSumGen(num, 0);
+    }
+
+    vector<vector<int> > threeSumGen(vector<int> &num, int target) {
+        vector<vector<int>> allSol;
+        if(num.size()<3) return allSol;
+        sort(num.begin(),num.end());
+
+        for(int i=0; i<num.size()-2; i++) {
+            if(i>0 && num[i]==num[i-1]) continue; // 去重
+
+            int left=i+1, right=num.size()-1;
+
+            while(left<right) {
+                int curSum = num[left]+num[right];
+                int curTarget = target-num[i];
+                if(curSum==curTarget) {
+                    vector<int> sol;
+                    sol.push_back(num[i]);
+                    sol.push_back(num[left]);
+                    sol.push_back(num[right]);
+                    allSol.push_back(sol);
+                    left++;
+                    right--;
+                    while(num[left]==num[left-1]) left++;
+                    while(num[right]==num[right+1]) right--;
+                }
+                else if(curSum<curTarget)
+                    left++;
+                else
+                    right--;
+            }
+        }
+        return allSol;
+    }
+
+
+
+//backtrace TLE  
+
+// 	vector<vector<int>> threeSum(vector<int>& nums) {
+// 		sort(nums.begin(), nums.end());
+// 		if (nums.size() <= 2 || nums[0] > 0) return{};
+// 		set<vector<int>> res;
+// 		for (int i = 0; i < nums.size(); i++)
+// 		{
+// 			int target = 0 - nums[i];
+// 			int m = 0, n = nums.size() - 1;
+// 			while (m < n)
+// 			{
+// 				while (true)
+// 				{
+//                     if (m >= n) break;
+// 					if (m == i)
+// 					{
+// 						m++;
+// 						continue;
+// 					}
+// 					if (n == i)
+// 					{
+// 						n--;
+// 						continue;
+// 					}
+// 					if (nums[m] + nums[n] == target) {
+// 						vector<int> s = { nums[m++], nums[i], nums[n] };
+// 						sort(s.begin(), s.end());
+//  						res.insert(s);
+// 						break;
+// 					}
+// 					if (nums[m] + nums[n] > target) n--;
+// 					if (nums[m] + nums[n] < target) m++;
+// 				}
+// 			}
+
+// 		}
+// 		vector<vector<int>> fres(res.begin(), res.end());
+// 		return fres;
+// 	}
+};
+
+// accelerate the cin process.
+int x = []() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(NULL);
+    return 0;
+}();