Dfs

Author: gzwl

Combinations/Combinations.cpp

@@ -0,0 +1,27 @@
+/*
+    比较基础的题，直接dfs k层就可以了，如果在当前层发现剩下的数凑不齐k个就回溯
+*/
+class Solution {
+public:
+    vector<vector<int> > combine(int n, int k) {
+        vector<vector<int> > res;
+        int *a = new int[k];
+        dfs(res,a,0,k,0,n);
+        delete [] a;
+        return res;
+    }
+    void dfs(vector<vector<int> > &res,int *a,int depth,int k,int cur,int n)
+    {
+        if(depth == k){
+            vector<int> tmp;
+            for(int i = 0;i < k;i++)    tmp.push_back(a[i]);
+            res.push_back(tmp);
+            return ;
+        }
+        for(int i = cur;i < n;i++){
+            if(n - cur < k - depth)     return ;    //剩下的数凑不齐k个，回溯
+            a[depth] = i + 1;
+            dfs(res,a,depth + 1,k,i + 1,n);
+        }
+    }
+};