Table of contents
Theoretical basis of backtracking algorithm
Theoretical basis of backtracking algorithm
In fact, when explaining the binary tree, I introduced backtracking to you. This time the backtracking algorithm is officially launched. You can watch the video first to have an overall understanding of the backtracking algorithm.
Topic link/article explanation: code caprice
Video explanation: Take you to learn the backtracking algorithm (theoretical articles) | Intensive lecture on the backtracking method! _哔哩哔哩_bilibili
77. Combination
Facing the code template given in The Theoretical Basis of Backtracking Algorithm, to do the combination problem of this question, everyone will find the routine of writing backtracking algorithm. In the process of backtracking algorithm to solve practical problems, you will have various questions. Watch the video introduction first, which can basically solve your doubts. The pruning operation in this question is the key point for everyone to understand, because many problems solved by backtracking algorithms in the future are all pruning routines.
Topic link/article explanation: code caprice
Problem solution idea:
the first time to write a backtracking algorithm, the pits inside have begun to be insufficient! ! ! A lot of details are worth noting. Here you can understand it not only by listening to Kage’s video, but you need to debug step by step to understand the backtracking algorithm in it.
class Solution {
LinkedList<Integer> path = new LinkedList<>();
List<List<Integer>> result = new ArrayList<>();
public List<List<Integer>> combine(int n, int k) {
backtracking(n, k, 1);
return result;
}
public void backtracking(int n, int k, int start){
if(path.size() == k){
result.add(new LinkedList<>(path)); //将 path 集合中的所有元素添加到新的集合中，因为path集合中的元素一直变化的，需要对符合条件的结果path复制一份到新的集合中
return;
}
for(int i = start; i <= n; i++){
path.add(i);
backtracking(n, k, i + 1);
path.removeLast(); //LinkedList集合所有的操作和双端队列差不多，能实现移除尾部元素操作，从而达到回溯目的，这里如果使用arraylist就不能实现删除尾部元素操作了！！！
}
}
}