Greedy

LeetCode 134 note: if total gas is short there is no answer; otherwise scan, and whenever the tank goes negative move the start to the next station

LeetCode 11 note: start pointers at both ends and always move the shorter side; moving the taller side only narrows the width without raising the height

LeetCode 1013 note: the total must be divisible by 3; accumulate from the left, cutting whenever the running sum hits total / 3, and succeed with at least 3 pieces

LeetCode 1005 note: negate the smallest value each time; once the smallest is positive, only the parity of the remaining count matters

LeetCode 942 note: two pointers hold the smallest and largest unused values; place the smallest on I and the largest on D

LeetCode 860 note: track only the counts of $5 and $10 bills; for $15 change prefer 10 + 5, since $5 bills are more versatile

LeetCode 680 note: at the first mismatch the only options are deleting the left or the right character; check whether either remainder is a palindrome

LeetCode 605 note: scan left to right and plant in any empty plot whose neighbors are empty; a new flower blocks the next plot, so actually update the array

LeetCode 561 note: sort and pair neighbors; each pair’s minimum is the element at an even index, so sum those

LeetCode 455 note: sort children and cookies, satisfying the least greedy child with the smallest cookie that suffices; each pointer walks once

LeetCode 409 note: use an even number of each character on the two sides, plus one in the middle if any count is odd