家里网络坏了,暂时无法上传图片
方法1: 这道题我尝试了好几个小时,做到后面越来越晕,都不知道自己在干嘛了。后来看了discussion的高票回答,觉得写得特别好,这边我给出链接。复杂度分析复盘的时候再看吧。
public class Solution {
public List<String> addOperators(String num, int target) {
List<String> rst = new ArrayList<String>();
if(num == null || num.length() == 0) return rst;
helper(rst, "", num, target, 0, 0, 0);
return rst;
}
public void helper(List<String> rst, String path, String num, int target, int pos, long eval, long multed){
if(pos == num.length()){
if(target == eval)
rst.add(path);
return;
}
for(int i = pos; i < num.length(); i++){
if(i != pos && num.charAt(pos) == '0') break;
long cur = Long.parseLong(num.substring(pos, i + 1));
if(pos == 0){
helper(rst, path + cur, num, target, i + 1, eval + cur, cur);
}
else{
helper(rst, path + "+" + cur, num, target, i + 1, eval + cur , cur);
helper(rst, path + "-" + cur, num, target, i + 1, eval -cur, -cur);
helper(rst, path + "*" + cur, num, target, i + 1, eval - multed + multed * cur, multed * cur );
}
}
}
}
总结:
- 无