Fix memory leak
Fix memory leak

00k/ToyDFS,00k/ToyDFS,lylei/dfs,yvxiang/coverage_for_bfs,yvxiang/dfs,yvxiang/coverage_for_bfs,imotai/bfs,bluebore/bfs,bluebore/dfs,myawan/bfs-1,yvxiang/dfs,bluebore/dfs,baidu/bfs,imotai/bfs,lylei/dfs,bluebore/bfs,myawan/bfs-1,bluebore/dfs,baidu/bfs,linyvxiang/dfs,linyvxiang/dfs,linyvxiang/dfs,yvxiang/dfs,baidu/bfs,yvxiang/dfs,lylei/dfs,yvxiang/coverage_for_bfs,yvxiang/coverage_for_bfs,myawan/bfs-1,baidu/bfs,bluebore/bfs,myawan/bfs-1,imotai/bfs,lylei/dfs