Binary-Tree

LeetCode 145 note: iterative post-order pushes a node back with a visited flag on its first pop, then the right and left children; record it on the second pop

LeetCode 112 note: subtract each value from targetSum on the way down; it works if the remainder matches at a leaf

LeetCode 111 note: minimum depth must end at a leaf; with only one child, the empty side (depth 0) cannot count as the minimum

LeetCode 110 note: every node’s subtree heights must differ by at most 1; return heights in post-order and propagate -1 once unbalanced

LeetCode 104 note: depth is 1 plus the larger subtree depth, with 0 for an empty tree

LeetCode 101 note: the left and right subtrees must mirror each other, outer with outer and inner with inner; compare values, not node objects

LeetCode 100 note: two empty trees are equal, one empty and one not differ, and otherwise compare values and recurse on both sides

LeetCode 94 note: iterative in-order traversal, pushing nodes while going left, recording on pop, then turning to the right subtree

LeetCode 144 note: iterative pre-order traversal records on pop and pushes the right child before the left so the left is handled first