题目:
给你一个由数字和运算符组成的字符串 expression
,按不同优先级组合数字和运算符,计算并返回所有可能组合的结果。你可以 按任意顺序 返回答案。
生成的测试用例满足其对应输出值符合 32 位整数范围,不同结果的数量不超过 104
。
示例 1:
输入:expression = "2-1-1"
输出:[0,2]
解释:
((2-1)-1) = 0
(2-(1-1)) = 2
示例 2:
输入:expression = "2*3-4*5"
输出:[-34,-14,-10,-10,10]
解释:
(2*(3-(4*5))) = -34
((2*3)-(4*5)) = -14
((2*(3-4))*5) = -10
(2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10
代码实现:
class Solution {
static final int ADDITION = -1;
static final int SUBTRACTION = -2;
static final int MULTIPLICATION = -3;
public List<Integer> diffWaysToCompute(String expression) {
List<Integer> ops = new ArrayList<Integer>();
for (int i = 0; i < expression.length();) {
if (!Character.isDigit(expression.charAt(i))) {
if (expression.charAt(i) == '+') {
ops.add(ADDITION);
} else if (expression.charAt(i) == '-') {
ops.add(SUBTRACTION);
} else {
ops.add(MULTIPLICATION);
}
i++;
} else {
int t = 0;
while (i < expression.length() && Character.isDigit(expression.charAt(i))) {
t = t * 10 + expression.charAt(i) - '0';
i++;
}
ops.add(t);
}
}
List<Integer>[][] dp = new List[ops.size()][ops.size()];
for (int i = 0; i < ops.size(); i++) {
for (int j = 0; j < ops.size(); j++) {
dp[i][j] = new ArrayList<Integer>();
}
}
return dfs(dp, 0, ops.size() - 1, ops);
}
public List<Integer> dfs(List<Integer>[][] dp, int l, int r, List<Integer> ops) {
if (dp[l][r].isEmpty()) {
if (l == r) {
dp[l][r].add(ops.get(l));
} else {
for (int i = l; i < r; i += 2) {
List<Integer> left = dfs(dp, l, i, ops);
List<Integer> right = dfs(dp, i + 2, r, ops);
for (int lv : left) {
for (int rv : right) {
if (ops.get(i + 1) == ADDITION) {
dp[l][r].add(lv + rv);
} else if (ops.get(i + 1) == SUBTRACTION) {
dp[l][r].add(lv - rv);
} else {
dp[l][r].add(lv * rv);
}
}
}
}
}
}
return dp[l][r];
}
}