Cruz would have to win the same battleground states that Trump will need:
Virginia, North Carolina, Florida, Colorado, Iowa, New Hampshire, Nevada, Wisconsin
http://www.270towin.com/maps/2016-election-battleground-states
If Cruz does not win Ohio or Florida there is no way in 40 hells he can get the nomination. The ONLY REASON he won a primary last night was because he was the only one that showed up in Idaho and for three weeks saturated the airways with anti-Trump lies. I live in Eastern Washington and I saw them every day. Before he showed up for the primary Cruz had never sat foot in Idaho. If Trump had wanted to carry the state he would have won going away. It was irrelevant to him. He still got 12 of the delegates, to 20 for Cruz.