while (i <= e1 && i <= e2) {
      const n1 = c1[i]
      const n2 = (c2[i] = optimized
        ? cloneIfMounted(c2[i] as VNode)
        : normalizeVNode(c2[i]))
        // 如果節(jié)點相同 則進行遞歸執(zhí)行patch更新節(jié)點
      if (isSameVNodeType(n1, n2)) {
        patch(
          n1,
          n2,
          container,
          null,
          parentComponent,
          parentSuspense,
          isSVG,
          slotScopeIds,
          optimized
        )
      } else {
        // 如果節(jié)點不相同，則直接退出
        break
      }
      i++
}

while (i <= e1 && i <= e2) {
      const n1 = c1[e1]
      const n2 = (c2[e2] = optimized
        ? cloneIfMounted(c2[e2] as VNode)
        : normalizeVNode(c2[e2]))
        // 如果是相同節(jié)點 則遞歸執(zhí)行patch
      if (isSameVNodeType(n1, n2)) {
        patch(
          n1,
          n2,
          container,
          null,
          parentComponent,
          parentSuspense,
          isSVG,
          slotScopeIds,
          optimized
        )
      } else {
        // 如果節(jié)點不相同 則退出
        break
      }
      e1--
      e2--
}

if (i > e1) {
      // 當索引大于老節(jié)點的尾部
      if (i <= e2) {
        // 當索引小于新節(jié)點的尾部 需要將剩余的節(jié)點添加
        const nextPos = e2 + 1
        const anchor = nextPos < l2 ? (c2[nextPos] as VNode).el : parentAnchor
        while (i <= e2) {
          patch(
            null,
            (c2[i] = optimized
              ? cloneIfMounted(c2[i] as VNode)
              : normalizeVNode(c2[i])),
            container,
            anchor,
            parentComponent,
            parentSuspense,
            isSVG,
            slotScopeIds,
            optimized
          )
          i++
        }
      }
}

else if (i > e2) {
      // 當索引i大于尾部索引e2 則直接刪除舊子樹從索引i開始到e1部分的節(jié)點
      while (i <= e1) {
        unmount(c1[i], parentComponent, parentSuspense, true)
        i++
      }
}

const s1 = i // prev starting index  舊子序列開始索引 從i開始記錄
const s2 = i // next starting index  新子序列開始索引 從i開始記錄

// 5.1 build key:index map for newChildren
// 根據(jù)key 建立新子序列的索引圖
const keyToNewIndexMap: Map<string | number | symbol, number> = new Map()
for (i = s2; i <= e2; i++) {
    // 獲取新節(jié)點
    const nextChild = (c2[i] = optimized
      ? cloneIfMounted(c2[i] as VNode)
      : normalizeVNode(c2[i]))
    if (nextChild.key != null) {
      if (__DEV__ && keyToNewIndexMap.has(nextChild.key)) {
        warn(
          `Duplicate keys found during update:`,
          JSON.stringify(nextChild.key),
          `Make sure keys are unique.`
        )
      }
      //  根據(jù)新節(jié)點的key 和 對應(yīng)的索引做映射關(guān)系
      // <key, index>
      keyToNewIndexMap.set(nextChild.key, i)
    }
}
let j
// 新子序列已經(jīng)更新的節(jié)點數(shù)量
let patched = 0
// 新子序列待更新節(jié)點的數(shù)量，等于新子序列的長度
const toBePatched = e2 - s2 + 1
// 是否存在需要移動的節(jié)點
let moved = false
// 用于跟蹤判斷是否有節(jié)點需要移動的節(jié)點
let maxNewIndexSoFar = 0
// 這個數(shù)組存儲新子序列中的元素在舊子序列節(jié)點出的索引，用于確定最長遞增子序列
const newIndexToOldIndexMap = new Array(toBePatched)
// 初始化數(shù)組 為0
// 0是一個特殊的值，如果遍歷之后仍有元素的值為0，則說明這個新節(jié)點沒有對應(yīng)的舊節(jié)點
for (i = 0; i < toBePatched; i++) newIndexToOldIndexMap[i] = 0

// 正序遍歷舊子序列
for (i = s1; i <= e1; i++) {
    const prevChild = c1[i]
    if (patched >= toBePatched) {
      // 所有新的子序列節(jié)點都已經(jīng)更新，刪除剩余的節(jié)點
      // all new children have been patched so this can only be a removal
      unmount(prevChild, parentComponent, parentSuspense, true)
      continue
    }

    let newIndex
    if (prevChild.key != null) {
      // 查找舊子序列中的節(jié)點在新子序列中的索引
      newIndex = keyToNewIndexMap.get(prevChild.key)
    } else {
      // key-less node, try to locate a key-less node of the same type
      for (j = s2; j <= e2; j++) {
        if (
          newIndexToOldIndexMap[j - s2] === 0 &&
          isSameVNodeType(prevChild, c2[j] as VNode)
        ) {
          newIndex = j
          break
        }
      }
    }
    if (newIndex === undefined) {
      // 找不到說明舊子序列需要刪除
      unmount(prevChild, parentComponent, parentSuspense, true)
    } else {
      // 更新新子序列中的元素在舊子序列中的索引，這里 +1 偏移是為了避免i為0的特殊情況 影響后面最長遞增子序列的求解
      newIndexToOldIndexMap[newIndex - s2] = i + 1
      //maxNewIndexSoFar 存儲的是上次舊值的newIndex 如果不是一直遞增 則說明有移動 
      if (newIndex >= maxNewIndexSoFar) {
        maxNewIndexSoFar = newIndex
      } else {
        moved = true
      }
      patch(
        prevChild,
        c2[newIndex] as VNode,
        container,
        null,
        parentComponent,
        parentSuspense,
        isSVG,
        slotScopeIds,
        optimized處
      )
      patched++
    }
}

const increasingNewIndexSequence = moved
        ? getSequence(newIndexToOldIndexMap)
        : EMPTY_ARR
j = increasingNewIndexSequence.length - 1
// 倒序遍歷 以便使用更新的節(jié)點作為錨點
for (i = toBePatched - 1; i >= 0; i--) {
    const nextIndex = s2 + i
    const nextChild = c2[nextIndex] as VNode
    // 錨點指向上一個更新的節(jié)點， 如果nextIndex超過新節(jié)點的長度，則指向parentAnchor
    const anchor =
      nextIndex + 1 < l2 ? (c2[nextIndex + 1] as VNode).el : parentAnchor
    if (newIndexToOldIndexMap[i] === 0) {
      // mount new
      // 掛載新節(jié)點
      patch(
        null,
        nextChild,
        container,
        anchor,
        parentComponent,
        parentSuspense,
        isSVG,
        slotScopeIds,
        optimized
      )
    } else if (moved) {
      // 沒有最長遞增子序列或者當前節(jié)點索引不在最長遞增子序列中， 需要移動
      if (j < 0 || i !== increasingNewIndexSequence[j]) {
        move(nextChild, container, anchor, MoveType.REORDER)
      } else {
        j--
      }
    }
}

// https://en.wikipedia.org/wiki/Longest_increasing_subsequence
function getSequence(arr: number[]): number[] {
  const p = arr.slice()
  const result = [0]
  let i, j, u, v, c
  const len = arr.length
  for (i = 0; i < len; i++) {
    // arrI 為當前順序取出的元素
    const arrI = arr[i]
    // 排除0的情況
    if (arrI !== 0) {
      // result 存儲的是長度為i的遞增子序列最小末尾值的索引 
      j = result[result.length - 1]
      // arr[j]為末位置，如果滿足arr[j]<arrI 那么直接在當前遞增子序列后面添加
      if (arr[j] < arrI) {
        // 存儲result更新前的最后一個索引的值
        p[i] = j
        // 存儲元素對應(yīng)的索引值
        result.push(i)
        continue
      }
      // 不滿足 則執(zhí)行二分搜索
      u = 0
      v = result.length - 1
      // 查找第一個比arrI小的節(jié)點，更新result的值
      while (u < v) {
        // c記錄中間的位置
        c = (u + v) >> 1
        if (arr[result[c]] < arrI) {
          // 若中間的值小于arrI 則在后邊 更新下沿
          u = c + 1
        } else {
          // 更新下沿
          v = c
        }
      }
      // 找到第一個比arrI小的位置u，插入它
      if (arrI < arr[result[u]]) {
        if (u > 0) {
          p[i] = result[u - 1]
        }
        result[u] = i
      }
    }
  }
  u = result.length
  v = result[u - 1]
  while (u-- > 0) {
    result[u] = v
    v = p[v]
  }
  return result
}