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Given?a?linked?list,?determine?if?it?has?a?cycle?in?it. Follow?up: Can?you?solve?it?without?using?extra?space?

題意：判斷鏈表有沒有環(huán)

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/** ?*?Definition?for?singly-linked?list. ?*?class?ListNode?{ ?*?????int?val; ?*?????ListNode?next; ?*?????ListNode(int?x)?{ ?*?????????val?=?x; ?*?????????next?=?null; ?*?????} ?*?} ?*/ public?class?Solution?{ ????public?boolean?hasCycle(ListNode?head)?{ ????????///定義兩個(gè)快慢指針。有環(huán)的話快指針一定會(huì)和慢指針相遇。否則快指針就提前到尾巴了 ????????應(yīng)該是我那會(huì)的考研題ca ????????if(head==null?||?head.next==null?||?head.next.next==null)return?false; ????????ListNode?fast=head.next.next; ????????ListNode?slow=head.next; ????????while(fast!=slow){ ????????????if(fast.next!=null?&&?fast.next.next!=null){ ????????????????fast=fast.next.next; ????????????????slow=slow.next;???? ????????????}else{ ????????????????//fast提前走到了尾 ????????????????return?false; ????????????} ????????????? ????????} ????????return?true; ????} }

PS：快慢指針。注意判斷邊界條件

本文轉(zhuǎn)自 努力的C 51CTO博客，原文鏈接:http://blog.51cto.com/fulin0532/1905474

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