前缀和
class NumArray {
public:
vectorsum;
NumArray(vector& nums) {
if(nums.size()>0){
sum.push_back(nums[0]);
}
for(int i=1;isum.push_back(sum[i-1] + nums[i]);
}
}
int sumRange(int i, int j) {
if( i==0 ){
return sum[j];
}else{
return sum[j] - sum[i-1];
}
return 0;
}
};