时间复杂度O(n)，空间复杂度O(1)
时间复杂度O(n)，空间复杂度O(1)
time:O(log n),space:O(1)
time:O(log n),space:O(1)
time:O(n),space:O(1)
time:O(n),space:O(1)
time:O(n),space:O(1)
Merge branch 'leetcode' of https://github.com/capricore/leetcode into leetcode