Merge pull request #19 from Liwb5/engine2.0

fix bug of random sample k

Author: seemingwang

paddle/fluid/distributed/table/graph/graph_weighted_sampler.cc

@@ -24,47 +24,33 @@ void RandomSampler::build(GraphEdgeBlob *edges) { this->edges = edges; }
 
 std::vector<int> RandomSampler::sample_k(int k, const std::shared_ptr<std::mt19937_64> rng) {
   int n = edges->size();
-  if (k > n) {
+  if (k >= n) {
     k = n;
-  }
-  std::vector<int> sample_result;
-  for(int i = 0;i < k;i ++ ) {
+    std::vector<int> sample_result;
+    for (int i = 0; i < k; i++) {
       sample_result.push_back(i);
+    }
+    return sample_result;
   }
-  if (k == n) {
-      return sample_result;
-  }
-
-  std::uniform_int_distribution<int> distrib(0, n - 1);
+  std::vector<int> sample_result;
   std::unordered_map<int, int> replace_map;
+  while (k--) {
+    std::uniform_int_distribution<int> distrib(0, n - 1);
+    int rand_int = distrib(*rng);
+    auto iter = replace_map.find(rand_int);
+    if (iter == replace_map.end()) {
+      sample_result.push_back(rand_int);
+    } else {
+      sample_result.push_back(iter->second);
+    }
 
-  for(int i = 0; i < k; i ++) {
-    int j = distrib(*rng);
-    if (j >= i) {
-      //  buff_nid[offset + i] = nid[j] if m.find(j) == m.end() else nid[m[j]]
-      auto iter_j = replace_map.find(j);
-      if(iter_j == replace_map.end()) {
-        sample_result[i] = j;
-      } else {
-        sample_result[i] = iter_j -> second;
-      }
-      //  m[j] = i if m.find(i) == m.end() else m[i]
-      auto iter_i = replace_map.find(i);
-      if(iter_i == replace_map.end()) {
-        replace_map[j] = i;
-      } else {
-        replace_map[j] = (iter_i -> second);
-      }
+    iter = replace_map.find(n - 1);
+    if (iter == replace_map.end()) {
+      replace_map[rand_int] = n - 1;
     } else {
-      sample_result[i] = sample_result[j];
-      // buff_nid[offset + j] = nid[i] if m.find(i) == m.end() else nid[m[i]] 
-      auto iter_i = replace_map.find(i);
-      if(iter_i == replace_map.end()) {
-        sample_result[j] = i;
-      } else {
-        sample_result[j] = (iter_i -> second);
-      }
+      replace_map[rand_int] = iter->second;
     }
+    --n;
   }
   return sample_result;
 }