1. Chinese dataset. http://www.mcm.edu.cn/html_cn/node/460baf68ab0ed0e1e557a0c79b1c4648.html.
2. The hungarian algorithm. https://www.geeksforgeeks.org/hungarian-algorithm-assignment-problem-set-1-introduction/.
3. Online workers unite. https://www.newscientist.com/article/mg21729036.200-crowdsourcing-grows-up-as-online-workers-unite/.
4. Unbalanced assignment problem. https://www.wisdomjobs.com/e-university/quantitative-techniques-for-management-tutorial-297/unbalanced-assignment-problem-9899.html.
5. Spatial crowdsourcing: Challenges and opportunities;Chen;IEEE Data Eng. Bull.,2016