题解 | #链表内指定区间反转#

/*
 * function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param head ListNode类 
 * @param m int整型 
 * @param n int整型 
 * @return ListNode类
 */
function reverseBetween( head ,  m ,  n ) {
    // write code here
    if (m === n ) {
        return head
    }
    let num = 0
    let p1 = head
    let startNode = null
    let lastNode = null
    let endNode = null
    let nextNode = null
    let left = null
    while (p1) {
        num++
        if(num === m) {
            startNode = p1
            lastNode = left
            if(num !== 1) {
                left.next = null
            }
        }
        if(num === n) {
            endNode = p1
            nextNode = p1.next
            p1.next = null
        }
        left = p1
        p1 = p1.next
    }
    //此时要反转startNode
    let last = null
    let p = startNode
    while (p) {
        let tem = p.next
        p.next = last
        last = p
        p = tem
    }
    //反转之后
    if(lastNode !== null) {
        lastNode.next = endNode
    }
    startNode.next = nextNode
    if (m === 1) {
        return endNode
    }
    return head
}
module.exports = {
    reverseBetween : reverseBetween
};